JP6006975B2 - Method for manufacturing semiconductor device - Google Patents

Description

The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device.

Note that in this specification, a semiconductor device refers to all devices that can function by utilizing semiconductor characteristics, and an electro-optical device, a semiconductor circuit, and an electronic device are all semiconductor devices.

A technique for forming a transistor (also referred to as a thin film transistor (TFT)) using a semiconductor thin film formed over a substrate having an insulating surface has attracted attention. The transistor is widely applied to electronic devices such as an integrated circuit (IC) and an image display device (display device). A silicon-based semiconductor material is widely known as a semiconductor thin film applicable to a transistor, but an oxide semiconductor has attracted attention as another material.

For example, a transistor using an amorphous oxide containing indium (In), gallium (Ga), and zinc (Zn) having an electron carrier concentration of less than 10 ¹⁸ / cm ³ as an active layer of the transistor is disclosed. (See Patent Document 1).

JP 2006-165528 A

However, when the oxide semiconductor is deviated from the stoichiometric composition or mixed with hydrogen or moisture forming an electron donor in the thin film formation process, its electrical conductivity changes. Such a phenomenon becomes a variation factor of electrical characteristics for a transistor including an oxide semiconductor.

In view of such problems, an object is to provide a semiconductor device including an oxide semiconductor with stable electrical characteristics and high reliability.

In a manufacturing process of a transistor including an oxide semiconductor film, an amorphous oxide semiconductor film is formed, and oxygen is introduced into the amorphous oxide semiconductor film to form an amorphous oxide semiconductor film containing excess oxygen. To do. After an aluminum oxide film is formed over the amorphous oxide semiconductor film, heat treatment is performed to crystallize at least part of the amorphous oxide semiconductor film, so that an oxide semiconductor film containing a crystal (crystalline oxide (Also referred to as a semiconductor film).

As an introduction method of oxygen (including at least one of oxygen radicals, oxygen atoms, and oxygen ions) into the amorphous oxide semiconductor film, an ion implantation method, an ion doping method, a plasma immersion ion implantation method, plasma Processing etc. can be used.

The crystalline oxide semiconductor film is an oxide semiconductor film that includes crystals and has crystallinity. The crystalline state of the crystalline oxide semiconductor film may be a state in which the directions of crystal axes are disordered or a state having a certain orientation.

In one embodiment of the invention disclosed in this specification, at least a part of the amorphous oxide semiconductor film is formed by performing heat treatment on the amorphous oxide semiconductor film in which oxygen is introduced and the aluminum oxide film is covered. Can be crystallized to form an oxide semiconductor film containing a crystal having a c-axis substantially perpendicular to the surface (crystalline oxide semiconductor film).

An oxide semiconductor film including a crystal having a c-axis substantially perpendicular to a surface has a structure which is not a single crystal structure or an amorphous structure, and is a crystalline oxide semiconductor having a c-axis orientation (C Axis aligned Crystalline Oxide Semiconductor (also referred to as CAAC-OS) film.

The CAAC-OS has c-axis orientation and a triangular or hexagonal atomic arrangement as viewed from the ab plane, surface, or interface direction. In the c-axis, a metal atom is a layered structure or a metal atom and an oxygen atom. Is an oxide semiconductor including crystals with different a-axis or b-axis orientations (rotated about the c-axis) on the ab plane (or surface or interface).

In a broad sense, CAAC-OS is a non-single crystal and has a triangular or hexagonal or equilateral triangular or hexagonal atomic arrangement when viewed from the direction perpendicular to the ab plane, and in the c-axis direction. A material containing a phase in which metal atoms are layered or metal atoms and oxygen atoms are arranged in layers as viewed from the vertical direction.

A CAAC-OS is not a single crystal but is not formed of only an amorphous substance. Further, although the CAAC-OS includes a crystallized portion (crystal portion), the boundary between one crystal portion and another crystal portion may not be clearly distinguished.

Part of oxygen included in the CAAC-OS may be replaced with nitrogen. In addition, the c-axis of each crystal part included in the CAAC-OS has a certain direction (eg, a direction perpendicular to a substrate surface on which the CAAC-OS film is formed, the surface, film surface, interface, or the like of the CAAC-OS film). It may be arranged. Alternatively, the normal line of the ab plane of each crystal part included in the CAAC-OS may face a certain direction (eg, a direction perpendicular to the substrate surface, the surface, the film surface, the interface, or the like).

By using the crystalline oxide semiconductor film, a change in electrical characteristics of the transistor due to irradiation with visible light or ultraviolet light can be further suppressed, and a highly reliable semiconductor device can be obtained.

Oxygen content of the oxide semiconductor film (amorphous oxide semiconductor film and crystalline oxide semiconductor film) is excessive with respect to the stoichiometric composition ratio in the crystalline state due to the oxygen introduction process. Are included. In this case, the oxygen content is set to exceed the stoichiometric composition ratio of the oxide semiconductor. Alternatively, the oxygen content is set to exceed the amount of oxygen in the case of a single crystal. Oxygen may exist between lattices of the oxide semiconductor. The composition of such an oxide semiconductor can be represented by InGaZn _m O _{m + 3x} (x> 1). For example, when m = 1, the composition of the oxide semiconductor is InGaZnO _{1 + 3x} (x> 1). When oxygen is excessive, 1 + 3x exceeds 4.

In the oxide semiconductor film, oxygen vacancies exist where oxygen is released. An oxide semiconductor that does not contain excess oxygen cannot be supplemented with other oxygen even if oxygen vacancies occur. However, a crystalline oxide semiconductor film according to one embodiment of the disclosed invention is a crystalline oxide semiconductor film containing excess oxygen (eg, a CAAC-OS film), and the crystalline oxide semiconductor film includes oxygen Even if a defect occurs, the excess oxygen in the film (preferably an excess of oxygen relative to the stoichiometric composition ratio) causes the excess oxygen to act on the defect part and immediately convert the oxygen to the defect part. Can be compensated.

The aluminum oxide film provided over the oxide semiconductor film has a blocking effect (blocking effect) that prevents the film from permeating both oxygen, impurities such as hydrogen, moisture, a hydroxyl group, or a hydride (also referred to as a hydrogen compound) and oxygen. high.

Therefore, an aluminum oxide film is a mixture of impurities such as hydrogen and moisture, which cause fluctuations, in an oxide semiconductor film during and after the manufacturing process, and an oxide of oxygen that is a main component material of the oxide semiconductor. It functions as a protective film that prevents emission from the semiconductor film.

In addition, since the heat treatment for crystallizing the amorphous oxide semiconductor film is performed in a state where the amorphous oxide semiconductor film is covered with the aluminum oxide film, the amorphous oxide semiconductor is obtained by the heat treatment for crystallization. Oxygen can be prevented from being released from the film. Therefore, the obtained crystalline oxide semiconductor film maintains the oxygen content of the amorphous oxide semiconductor film, and the oxide semiconductor has an excessive oxygen content with respect to the stoichiometric composition ratio in the crystalline state. The film can include a region.

Therefore, the formed crystalline oxide semiconductor film has high purity because impurities such as hydrogen and moisture and the release of excessively introduced oxygen are prevented by the aluminum oxide film. A region where the oxygen content is excessive relative to the stoichiometric composition ratio in the crystalline state is included.

Therefore, when the crystalline oxide semiconductor film is used for a transistor, variation in threshold voltage Vth of the transistor due to oxygen vacancies and shift ΔVth in threshold voltage can be reduced.

In addition, dehydration or dehydrogenation by heat treatment in which impurities such as hydrogen atoms or impurities including hydrogen atoms such as water are intentionally excluded from the oxide semiconductor film before the formation of the aluminum oxide film is performed. It is preferable to perform the conversion treatment.

Hydrogen is removed from the oxide semiconductor, purified so as not to contain impurities as much as possible, and filled with oxygen vacancies to make it an I-type (intrinsic) oxide semiconductor, or an oxide close to I-type (intrinsic) It can be a semiconductor. That is, by removing impurities such as hydrogen and water as much as possible and filling oxygen vacancies, highly purified type I (intrinsic semiconductor) or the like can be obtained. By doing so, the Fermi level (Ef) of the oxide semiconductor can be brought to the same level as the intrinsic Fermi level (Ei).

One embodiment of the structure of the invention disclosed in this specification includes an insulating film, an aluminum oxide film, an amorphous oxide semiconductor film sandwiched between the insulating film and the aluminum oxide film, and the amorphous film. A heat treatment is performed on the crystalline oxide semiconductor film to crystallize at least part thereof to form an oxide semiconductor film containing crystals. The amorphous oxide semiconductor film is implanted with oxygen, and the oxide semiconductor is crystallized. This is a method for manufacturing a semiconductor device in which a region where the oxygen content is excessive with respect to the stoichiometric composition ratio in the state is included.

In one embodiment of the structure of the invention disclosed in this specification, an insulating film is formed, an amorphous oxide semiconductor film is formed over the insulating film, oxygen is injected into the amorphous oxide semiconductor film, An aluminum oxide film is formed over the oxygen-implanted amorphous oxide semiconductor film, and the amorphous oxide semiconductor film into which oxygen has been implanted is subjected to heat treatment to crystallize at least part thereof to include crystals. The amorphous oxide semiconductor film into which the oxide semiconductor film is formed and oxygen is implanted includes a region in which the oxygen content is excessive with respect to the stoichiometric composition ratio in the crystalline state. This is a method for manufacturing a semiconductor device.

In one embodiment of the structure of the invention disclosed in this specification, an insulating film is formed, an amorphous oxide semiconductor film is formed over the insulating film, and an aluminum oxide film is formed over the amorphous oxide semiconductor film. Forming, passing through the aluminum oxide film, injecting oxygen into the amorphous oxide semiconductor film, and subjecting the amorphous oxide semiconductor film into which oxygen has been injected to heat treatment to crystallize at least a part thereof. In the amorphous oxide semiconductor film in which oxygen is implanted, the oxide semiconductor has an oxygen content that is excessive with respect to the stoichiometric composition ratio in the crystalline state. This is a method for manufacturing a semiconductor device including a region.

In one embodiment of the present invention, a semiconductor device including transistors with various structures such as a top gate structure, a bottom gate structure, a staggered structure, or a planar structure can be manufactured. Further, in the step of introducing oxygen into the amorphous oxide semiconductor film, oxygen may be directly introduced into the exposed amorphous oxide semiconductor film, and another film may be formed on the amorphous oxide semiconductor film. Alternatively, oxygen may be passed through the film and introduced into the amorphous oxide semiconductor film. Depending on the structure of the transistor, even if the step of introducing oxygen into the amorphous oxide semiconductor film in the manufacturing process of the semiconductor device is performed on the exposed amorphous oxide semiconductor film, the amorphous oxide semiconductor An insulating film (a gate insulating film, an insulating film (including an aluminum oxide film), or a stacked layer of a gate insulating film and an insulating film (including an aluminum oxide film)), or a stacked layer of a gate insulating film and a gate electrode layer is formed over the film. This can be performed even for the amorphous oxide semiconductor film formed.

In the above structure, the oxide semiconductor film including a crystal obtained by crystallization by heat treatment is a crystalline oxide semiconductor (CAAC-OS) film including a crystal having a c-axis substantially perpendicular to the surface. It is preferable.

In the insulating film, a region formed in contact with the amorphous oxide semiconductor film is preferably a surface with reduced surface roughness. Specifically, the average surface roughness of the insulating film surface is 1 nm or less, preferably 0.3 nm or less, more preferably 0.1 nm or less. By forming the oxide semiconductor film on the surface of the insulating film with reduced surface roughness, an oxide semiconductor film having stable and favorable crystallinity can be obtained.

In the above structure, an oxide insulating film may be formed between the gate electrode layer and the aluminum oxide film. A sidewall insulating layer having a sidewall structure that covers the side surface of the gate electrode layer may be formed before the formation of the aluminum oxide film.

In the above structure, heat treatment for releasing hydrogen or moisture may be performed on the amorphous oxide semiconductor film before the oxygen introduction step and the aluminum oxide film formation step.

In this manner, a transistor including a crystalline oxide semiconductor film which is highly purified and contains oxygen excessively to fill oxygen vacancies is suppressed in electrical characteristics and is electrically stable. Thus, a highly reliable semiconductor device including an oxide semiconductor having stable electrical characteristics can be provided.

By providing an aluminum oxide film over the crystalline oxide semiconductor film so that excess oxygen contained in the oxide semiconductor film is not released by heat treatment, the interface between the crystalline oxide semiconductor and a layer that is in contact with the upper and lower layers is provided. It is possible to prevent defects from being generated and increasing. That is, excess oxygen contained in the crystalline oxide semiconductor film acts to fill oxygen vacancy defects, so that a highly reliable semiconductor device having stable electric characteristics can be provided.

Thus, according to one embodiment of the disclosed invention, a transistor having stable electrical characteristics can be manufactured.

Further, according to one embodiment of the disclosed invention, a highly reliable semiconductor device with favorable electrical characteristics can be manufactured.

8A and 8B illustrate one embodiment of a semiconductor device and a method for manufacturing the semiconductor device. 8A and 8B illustrate one embodiment of a semiconductor device and a method for manufacturing the semiconductor device. 8A and 8B illustrate one embodiment of a semiconductor device and a method for manufacturing the semiconductor device. 8A and 8B illustrate one embodiment of a semiconductor device and a method for manufacturing the semiconductor device. 8A and 8B illustrate one embodiment of a semiconductor device and a method for manufacturing the semiconductor device. 8A and 8B illustrate one embodiment of a semiconductor device and a method for manufacturing the semiconductor device. 8A and 8B illustrate one embodiment of a semiconductor device and a method for manufacturing the semiconductor device. 8A and 8B illustrate one embodiment of a semiconductor device and a method for manufacturing the semiconductor device. 8A and 8B illustrate one embodiment of a semiconductor device and a method for manufacturing the semiconductor device. 6A and 6B illustrate one embodiment of a semiconductor device. 6A and 6B illustrate one embodiment of a semiconductor device. 6A and 6B illustrate one embodiment of a semiconductor device. 6A and 6B illustrate one embodiment of a semiconductor device. 6A and 6B illustrate one embodiment of a semiconductor device. 6A and 6B illustrate one embodiment of a semiconductor device. FIG. 9 illustrates an electronic device. The figure which shows the SIMS measurement result of the comparative example sample A. The figure which shows the SIMS measurement result of Example sample A. The figure which shows the TDS measurement result of the comparative example sample B. The figure which shows the TDS measurement result of the Example sample B.

Hereinafter, embodiments of the invention disclosed in this specification will be described in detail with reference to the drawings. However, the invention disclosed in this specification is not limited to the following description, and it is easily understood by those skilled in the art that modes and details can be variously changed. Further, the invention disclosed in this specification is not construed as being limited to the description of the embodiments below. In addition, the ordinal numbers attached as the first and second are used for convenience and do not indicate the order of steps or the order of lamination. In addition, a specific name is not shown as a matter for specifying the invention in this specification.

(Embodiment 1)
In this embodiment, one embodiment of a semiconductor device and a method for manufacturing the semiconductor device will be described with reference to FIGS. In this embodiment, a transistor including an oxide semiconductor film is described as an example of a semiconductor device.

There is no particular limitation on the structure of the transistor, and a top gate structure, a bottom gate structure, a staggered type, a planar type, or the like can be used, for example. The transistor may have a single gate structure in which one channel formation region is formed, a double gate structure in which two channel formation regions are formed, or a triple gate structure in which three channel formation regions are formed. Alternatively, a dual gate type having two gate electrode layers disposed above and below the channel region with a gate insulating film interposed therebetween may be used.

As illustrated in FIG. 1E, the transistor 410 includes a gate electrode layer 401, a gate insulating film 402, a crystalline oxide semiconductor film 403, a source electrode layer 405a, and a drain electrode layer 405b over a substrate 400 having an insulating surface. including. An insulating film 407 is formed over the transistor 410.

The insulating film 407 may be a single layer or a stacked layer, but has a structure including an aluminum oxide film. In this embodiment, the gate insulating film 402 is a silicon oxide film, and the insulating film 407 is an aluminum oxide film.

The crystalline oxide semiconductor film 403 is a crystalline oxide semiconductor film containing crystals. The crystalline oxide semiconductor film 403 is an oxide semiconductor film including a crystal having an ab plane parallel to the surface and a c-axis substantially perpendicular to the surface. It is preferably a crystalline oxide semiconductor (CAAC) that has a c-axis orientation and has neither a structure nor an amorphous structure. By using a crystalline oxide semiconductor film, a change in electrical characteristics of the transistor 410 due to irradiation with visible light or ultraviolet light can be further suppressed, so that a highly reliable semiconductor device can be obtained.

FIGS. 1A to 1E illustrate an example of a method for manufacturing the transistor 410.

First, after a conductive film is formed over the substrate 400 having an insulating surface, the gate electrode layer 401 is formed by a first photolithography process. Note that the resist mask may be formed by an inkjet method. When the resist mask is formed by an ink-jet method, a manufacturing cost can be reduced because a photomask is not used.

There is no particular limitation on a substrate that can be used as the substrate 400 having an insulating surface as long as it has heat resistance enough to withstand heat treatment performed later. For example, a glass substrate such as barium borosilicate glass or alumino borosilicate glass, a ceramic substrate, a quartz substrate, a sapphire substrate, or the like can be used. In addition, a single crystal semiconductor substrate such as silicon or silicon carbide, a polycrystalline semiconductor substrate, a compound semiconductor substrate such as silicon germanium, an SOI substrate, or the like can be applied, and a semiconductor element provided on these substrates, The substrate 400 may be used.

Alternatively, a semiconductor device may be manufactured using a flexible substrate as the substrate 400. In order to manufacture a flexible semiconductor device, the transistor 410 including the crystalline oxide semiconductor film 403 may be directly formed over a flexible substrate, or the crystalline oxide semiconductor film may be formed over another manufacturing substrate. The transistor 410 including the transistor 403 may be manufactured, and then peeled and transferred to the flexible substrate. Note that in order to separate the transistor from the manufacturing substrate and transfer it to the flexible substrate, a separation layer may be provided between the manufacturing substrate and the transistor including the oxide semiconductor film.

An insulating film serving as a base film may be provided between the substrate 400 and the gate electrode layer 401. The base film has a function of preventing diffusion of impurity elements from the substrate 400, and has a stacked structure of one or more films selected from a silicon nitride film, a silicon oxide film, a silicon nitride oxide film, and a silicon oxynitride film. Can be formed.

The gate electrode layer 401 is made of a metal material such as molybdenum, titanium, tantalum, tungsten, aluminum, copper, neodymium, or scandium or an alloy material containing these as a main component by a plasma CVD method or a sputtering method. It can be formed as a single layer or stacked layers.

The material of the gate electrode layer 401 is indium tin oxide, indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, indium A light-transmitting conductive material such as zinc oxide or indium tin oxide to which silicon oxide is added, or a nitride of a light-transmitting conductive material can also be used. Alternatively, a stacked structure of the above light-transmitting conductive material and the above metal material can be employed.

In addition, the gate electrode layer 401 has a stacked structure, and one layer thereof includes In—Sn—O, In—Sn—Zn—O, In—Al—Zn—O, Sn—Ga—Zn—O, and Al. -Ga-Zn-O, Sn-Al-Zn-O, In-Zn-O, Sn-Zn-O, Al-Zn-O, In-O, Sn-O, Zn- An O-based metal oxide may be used. It is preferable that the gate electrode layer 401 have a stacked structure and an oxynitride film (also referred to as an IGZON film) containing indium, gallium, and zinc, which is a material having a particularly high work function, be used as one layer. An oxynitride film containing indium, gallium, and zinc can be obtained by forming a film in a mixed gas atmosphere of argon and nitrogen.

For example, a stacked structure of a copper film, a tungsten film, and an oxynitride film (IGZON film) containing indium, gallium, and zinc as the gate electrode layer 401 from the substrate 400 side, a tungsten film, a tungsten nitride film, and a copper A stacked structure of a film and a titanium film can be used.

Next, the gate insulating film 402 is formed over the gate electrode layer 401 by a plasma CVD method, a sputtering method, or the like. As a material of the gate insulating film 402, a silicon oxide film, a gallium oxide film, an aluminum oxide film, a silicon nitride film, a silicon oxynitride film, an aluminum oxynitride film, or a silicon nitride oxide film can be used.

As materials for the gate insulating film 402, hafnium oxide, yttrium oxide, hafnium silicate (HfSi _x O _y (x> 0, y> 0)), hafnium silicate to which nitrogen is added (HfSiO _x N _y (x> 0, The gate leakage current can be reduced by using a high-k material such as y> 0)), hafnium aluminate (HfAl _x O _y (x> 0, y> 0)), or lanthanum oxide.

Although the gate insulating film 402 may be a single layer or a stacked layer, an oxide insulating film is preferable as the film in contact with the crystalline oxide semiconductor film 403. In this embodiment, a silicon oxide film is used as the gate insulating film 402.

Since the gate insulating film 402 is in contact with the crystalline oxide semiconductor film 403, it is preferable that an amount of oxygen exceeding the stoichiometric ratio exists in the film (in the bulk). Such a region where oxygen content is excessive (oxygen-excess region) only needs to exist in a part of the gate insulating film 402 (including the interface). For example, when a silicon oxide film is used as the gate insulating film 402, SiO _{2 + α} (where α> 0) is set.

By setting the silicon oxide film in contact with the crystalline oxide semiconductor film 403 to a state containing a large amount of oxygen, the silicon oxide film can function suitably as a supply source for supplying oxygen to the oxide semiconductor film.

Therefore, by using such a gate insulating film 402, oxygen can be supplied to the crystalline oxide semiconductor film 403, and the characteristics can be improved. By supplying oxygen to the crystalline oxide semiconductor film 403, oxygen vacancies in the film can be filled.

A gate insulating film 402 containing a large amount (excess) of oxygen serving as an oxygen supply source is provided in contact with the crystalline oxide semiconductor film 403 so that oxygen is supplied from the gate insulating film 402 to the crystalline oxide semiconductor film 403. can do. For example, oxygen can be supplied to the crystalline oxide semiconductor film 403 by performing the heating step with at least part of the crystalline oxide semiconductor film 403 and the gate insulating film 402 being in contact with each other.

In order to prevent hydrogen, a hydroxyl group, and moisture from being contained in the gate insulating film 402 and the oxide semiconductor film formed over the gate insulating film 402 as much as possible, sputtering is performed as a pretreatment for forming the oxide semiconductor film. In the preheating chamber of the apparatus, the substrate 400 on which the gate electrode layer 401 is formed or the substrate 400 on which the gate insulating film 402 is formed is preheated, and impurities such as hydrogen and moisture adsorbed on the substrate 400 are desorbed and exhausted. It is preferable. Note that a cryopump is preferable as an exhaustion unit provided in the preheating chamber. Note that this preheating treatment can be omitted. Further, this preheating may be similarly performed on the substrate 400 over which the source electrode layer 405a and the drain electrode layer 405b are formed before the insulating film 407 is formed.

Note that before the amorphous oxide semiconductor film 491 is formed by a sputtering method, reverse sputtering in which an argon gas is introduced to generate plasma is performed, so that a powdery substance attached to the surface of the gate insulating film 402 ( It is preferable to remove particles (also referred to as particles or dust). Inverse sputtering is a method of modifying the surface by forming a plasma near the substrate by applying a voltage to the substrate side using an RF power source in an argon atmosphere without applying a voltage to the target side. Note that nitrogen, helium, oxygen, or the like may be used instead of the argon atmosphere.

Next, an amorphous oxide semiconductor film 491 with a thickness of 2 nm to 200 nm, preferably 5 nm to 30 nm is formed over the gate insulating film 402 (see FIG. 1A).

As a method for forming the amorphous oxide semiconductor film 491, a sputtering method, an MBE (Molecular Beam Epitaxy) method, a CVD method, a pulse laser deposition method, an ALD (Atomic Layer Deposition) method, or the like can be used as appropriate. Further, the amorphous oxide semiconductor film 491 is formed using a sputtering apparatus that forms a film in a state where a plurality of substrate surfaces are set substantially perpendicular to the surface of the sputtering target, a so-called CP sputtering apparatus (Column Plasma Sputtering system). You may form into a film.

An oxide semiconductor used for the amorphous oxide semiconductor film 491 preferably contains at least indium (In) or zinc (Zn). In particular, In and Zn are preferably included. In addition, it is preferable that gallium (Ga) be included in addition to the stabilizer for reducing variation in electrical characteristics of the transistor including the oxide semiconductor. Moreover, it is preferable to have tin (Sn) as a stabilizer. Moreover, it is preferable to have hafnium (Hf) as a stabilizer. Moreover, it is preferable to have aluminum (Al) as a stabilizer.

Other stabilizers include lanthanoids such as lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), and terbium (Tb). , Dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), or lutetium (Lu).

For example, as an oxide semiconductor, indium oxide, tin oxide, zinc oxide, binary metal oxides such as In—Zn oxide, Sn—Zn oxide, Al—Zn oxide, Zn—Mg oxide Oxides, Sn—Mg oxides, In—Mg oxides, In—Ga oxides, In—Ga—Zn oxides (also referred to as IGZO) which are oxides of ternary metals, In— Al-Zn oxide, In-Sn-Zn oxide, Sn-Ga-Zn oxide, Al-Ga-Zn oxide, Sn-Al-Zn oxide, In-Hf-Zn oxide In-La-Zn-based oxide, In-Ce-Zn-based oxide, In-Pr-Zn-based oxide, In-Nd-Zn-based oxide, In-Sm-Zn-based oxide, In-Eu -Zn oxide, In-Gd-Zn oxide, In-Tb-Zn oxide, n-Dy-Zn-based oxide, In-Ho-Zn-based oxide, In-Er-Zn-based oxide, In-Tm-Zn-based oxide, In-Yb-Zn-based oxide, In-Lu-Zn -Based oxides, In-Sn-Ga-Zn-based oxides that are oxides of quaternary metals, In-Hf-Ga-Zn-based oxides, In-Al-Ga-Zn-based oxides, In-Sn- An Al—Zn-based oxide, an In—Sn—Hf—Zn-based oxide, or an In—Hf—Al—Zn-based oxide can be used.

Note that here, for example, an In—Ga—Zn-based oxide means an oxide containing In, Ga, and Zn as its main components, and there is no limitation on the ratio of In, Ga, and Zn. Moreover, metal elements other than In, Ga, and Zn may be contained.

Alternatively, a material represented by InMO ₃ (ZnO) _m (m> 0 is satisfied, and m is not an integer) may be used as the oxide semiconductor. Note that M represents one metal element or a plurality of metal elements selected from Ga, Fe, Mn, and Co. Alternatively, a material represented by In ₂ SnO ₅ (ZnO) _n (n> 0 is satisfied, and n is an integer) may be used as the oxide semiconductor.

For example, In: Ga: Zn = 1: 1: 1 (= 1/3: 1/3: 1/3) or In: Ga: Zn = 2: 2: 1 (= 2/5: 2/5: 1). / 5) atomic ratio In—Ga—Zn-based oxides and oxides in the vicinity of the composition can be used. Alternatively, In: Sn: Zn = 1: 1: 1 (= 1/3: 1/3: 1/3), In: Sn: Zn = 2: 1: 3 (= 1/3: 1/6: 1) / 2) or In: Sn: Zn = 2: 1: 5 (= 1/4: 1/8: 5/8) atomic ratio In—Sn—Zn-based oxide or an oxide in the vicinity of the composition. Use it.

However, the composition is not limited thereto, and a material having an appropriate composition may be used depending on required semiconductor characteristics (mobility, threshold value, variation, etc.). In order to obtain the required semiconductor characteristics, it is preferable that the carrier concentration, impurity concentration, defect density, atomic ratio of metal element to oxygen, interatomic bond distance, density, and the like are appropriate.

For example, high mobility can be obtained relatively easily with an In—Sn—Zn-based oxide.

Note that for example, the composition of an oxide in which the atomic ratio of In, Ga, and Zn is In: Ga: Zn = a: b: c (a + b + c = 1) has an atomic ratio of In: Ga: Zn = A: B: being in the vicinity of the oxide composition of C (A + B + C = 1), a, b and c are (a−A) ² + (b−B) ² + (c−C) ² ≦ r ² R may be 0.05, for example. The same applies to other oxides.

The crystalline oxide semiconductor film 403 which is an oxide semiconductor having crystallinity can further reduce defects in the bulk and can obtain higher mobility than an oxide semiconductor in an amorphous state if surface flatness is increased. it can. In order to improve the flatness of the surface, it is preferable to form an oxide semiconductor on the flat surface. Specifically, the average surface roughness (Ra) is 1 nm or less, preferably 0.3 nm or less, more preferably Is preferably formed on a surface of 0.1 nm or less.

Ra is a three-dimensional extension of the centerline average roughness defined in JIS B0601 so that it can be applied to a surface. “A value obtained by averaging the absolute values of deviations from a reference surface to a specified surface” "And is defined by the following equation.

In the above, S ₀ is surrounded by four points represented by the measurement plane (coordinates (x ₁ , y ₁ ) (x ₁ , y ₂ ) (x ₂ , y ₁ ) (x ₂ , y ₂ )). (Rectangular region) indicates the area, and Z ₀ indicates the average height of the measurement surface. Ra can be evaluated with an atomic force microscope (AFM).

Therefore, planarization treatment may be performed on a region where the crystalline oxide semiconductor film 403 (the amorphous oxide semiconductor film 491 in FIG. 1A) is formed in contact with the gate insulating film 402. The planarization treatment is not particularly limited, and polishing treatment (for example, chemical mechanical polishing (CMP) method), dry etching treatment, or plasma treatment can be used.

As the plasma treatment, for example, reverse sputtering in which an argon gas is introduced to generate plasma can be performed.

As the planarization treatment, the polishing treatment, the dry etching treatment, and the plasma treatment may be performed a plurality of times or in combination. In the case of performing the combination, the order of steps is not particularly limited, and may be set as appropriate in accordance with the uneven state of the surface of the gate insulating film 402.

In this embodiment, the amorphous oxide semiconductor film 491 is formed by a sputtering method with the use of an In—Ga—Zn-based metal oxide target. The atmosphere for forming the amorphous oxide semiconductor film 491 can be a rare gas (typically argon) atmosphere, an oxygen atmosphere, or a mixed atmosphere of a rare gas and oxygen. .

Note that the amorphous oxide semiconductor film 491 is formed under such a condition that a large amount of oxygen is contained during film formation (for example, film formation is performed by a sputtering method in an atmosphere containing 100% oxygen). A film containing a large amount (preferably including a region in which an oxygen content is excessive with respect to a stoichiometric composition ratio of the oxide semiconductor in a crystalline state) is preferable.

As a target for forming the oxide semiconductor film by a sputtering method, for example, an oxide target having a composition ratio of In ₂ O ₃ : Ga ₂ O ₃ : ZnO = 1: 1: 2 [mol ratio] is used. An In—Ga—Zn film is formed. Without limitation to the material and the composition of the target, for _{example, In 2 O 3: Ga 2} O 3: ZnO = 1: 1: 1 may be used a metal oxide target [mol ratio].

The filling rate of the metal oxide target is 90% to 100%, preferably 95% to 99.9%. By using a metal oxide target with a high filling rate, the formed oxide semiconductor film can be a dense film.

As a sputtering gas used for forming the oxide semiconductor film, a high-purity gas from which impurities such as hydrogen, water, a hydroxyl group, or hydride are removed is preferably used.

The substrate is held in a film formation chamber held in a reduced pressure state. Then, a sputtering gas from which hydrogen and moisture are removed is introduced while moisture remaining in the deposition chamber is removed, and an amorphous oxide semiconductor film 491 is formed over the substrate 400 using the target. In order to remove moisture remaining in the deposition chamber, it is preferable to use an adsorption-type vacuum pump such as a cryopump, an ion pump, or a titanium sublimation pump. Further, the exhaust means may be a turbo molecular pump provided with a cold trap. In the film formation chamber evacuated using a cryopump, for example, a compound containing a hydrogen atom (more preferably a compound containing a carbon atom) such as a hydrogen atom or water (H ₂ O) is exhausted. The concentration of impurities contained in the amorphous oxide semiconductor film 491 formed in the chamber can be reduced.

The gate insulating film 402 and the amorphous oxide semiconductor film 491 are preferably formed continuously without being released to the atmosphere. When the gate insulating film 402 and the amorphous oxide semiconductor film 491 are formed successively without being exposed to the air, impurities such as hydrogen and moisture can be prevented from being adsorbed on the surface of the gate insulating film 402.

Further, heat treatment for removing (dehydrating or dehydrogenating) excess hydrogen (including water and a hydroxyl group) may be performed on the amorphous oxide semiconductor film 491. The temperature of the heat treatment is a temperature at which the amorphous oxide semiconductor film is not crystallized, and is typically 250 ° C to 400 ° C, preferably 300 ° C.

Note that the heat treatment for dehydration or dehydrogenation is performed after the formation of the amorphous oxide semiconductor film 491 and before the step of introducing oxygen into the amorphous oxide semiconductor film 491. It may be performed at any timing.

In addition, when the heat treatment for dehydration or dehydrogenation is performed before the amorphous oxide semiconductor film 491 is processed into an island shape, oxygen contained in the gate insulating film 402 is released by the heat treatment. Since it can prevent, it is preferable.

Note that in the heat treatment, it is preferable that water, hydrogen, or the like be not contained in nitrogen or a rare gas such as helium, neon, or argon. Alternatively, the purity of nitrogen or a rare gas such as helium, neon, or argon introduced into the heat treatment apparatus is 6N (99.9999%) or more, preferably 7N (99.99999%) or more (that is, the impurity concentration is 1 ppm or less, preferably Is preferably 0.1 ppm or less).

In addition, after the amorphous oxide semiconductor film 491 is heated by heat treatment, a high-purity oxygen gas, a high-purity oxygen dinitride gas, or ultra-dry air (CRDS (cavity ring-down laser spectroscopy) method) is used in the same furnace. The amount of water when measured using a dew point meter of 20 ppm (dew point conversion -55 ° C.) or less, preferably 1 ppm or less, preferably 10 ppb or less) may be introduced. It is preferable that water, hydrogen, or the like be not contained in the oxygen gas or the oxygen dinitride gas. Alternatively, the purity of the oxygen gas or oxygen dinitride gas introduced into the heat treatment apparatus is 6 N or more, preferably 7 N or more (that is, the impurity concentration in the oxygen gas or oxygen dinitride gas is 1 ppm or less, preferably 0.1 ppm or less). It is preferable to do. By supplying oxygen, which is a main component material of the amorphous oxide semiconductor, which has been simultaneously reduced by the process of removing impurities by dehydration or dehydrogenation treatment by the action of oxygen gas or oxygen dinitride gas Thus, the amorphous oxide semiconductor film can be highly purified and can be electrically i-type (intrinsic).

Next, oxygen 431 (including at least one of oxygen radicals, oxygen atoms, and oxygen ions) is introduced into the amorphous oxide semiconductor film 491 so that oxygen is supplied to the amorphous oxide semiconductor film 491. Do. As a method for introducing oxygen, an ion implantation method, an ion doping method, a plasma immersion ion implantation method, a plasma treatment, or the like can be used.

In the manufacturing process of the transistor 410 in this embodiment, the oxygen introduction step is performed after the amorphous oxide semiconductor film 491 is formed and before the aluminum oxide film is formed as the insulating film 407. Note that heat treatment for dehydration or dehydrogenation is performed before the oxygen introduction step. The oxygen introduction step may be directly introduced into the amorphous oxide semiconductor film, or may be introduced into the amorphous oxide semiconductor film through another film such as a gate insulating film or an insulating film. Also good. When oxygen is introduced into an amorphous oxide semiconductor film through another film, an ion implantation method, an ion doping method, a plasma immersion ion implantation method, or the like may be used, as in this embodiment mode In the case where oxygen is directly introduced into the exposed amorphous oxide semiconductor film 491, plasma treatment or the like can be used.

In this embodiment, oxygen 431 is implanted into the amorphous oxide semiconductor film 491 by an ion implantation method. Through the implantation process of oxygen 431, the amorphous oxide semiconductor film 491 is formed into an amorphous oxide film in which an oxide semiconductor includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio in a crystalline state. The semiconductor film 441 is formed (see FIG. 1B).

For example, it is preferable that the oxygen concentration in the amorphous oxide semiconductor film 441 introduced in the step of introducing oxygen 431 be 1 × 10 ¹⁸ / cm ³ or more and 3 × 10 ²¹ / cm ³ or less. Note that the oxygen-excess region only needs to exist in part (including the interface) of the amorphous oxide semiconductor film 441. Therefore, by introducing oxygen 431, in the stack of the gate insulating film 402, the amorphous oxide semiconductor film 441, and the insulating film 407, an interface between the gate insulating film 402 and the amorphous oxide semiconductor film 441, non- Oxygen is contained in the crystalline oxide semiconductor film 441 or at least one of the interfaces between the amorphous oxide semiconductor film 441 and the insulating film 407.

The amorphous oxide semiconductor film 441 includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio of the oxide semiconductor in a crystalline state. In this case, the oxygen content is set to exceed the stoichiometric composition ratio of the oxide semiconductor. Alternatively, the oxygen content is set to exceed the amount of oxygen in the case of a single crystal. Oxygen may exist between lattices of the oxide semiconductor. The composition of such an oxide semiconductor can be represented by InGaZn _m O _{m + 3x} (x> 1). For example, when m = 1, the composition of the oxide semiconductor is InGaZnO _{1 + 3x} (x> 1). When oxygen is excessive, 1 + 3x exceeds 4.

Oxygen vacancies existing in the amorphous oxide semiconductor film 441 can be filled with the supplied oxygen 431.

Note that the amorphous state in the amorphous oxide semiconductor film 441 can be made more uniform by the step of introducing oxygen 431.

Note that oxygen is one of main component materials in an oxide semiconductor. Therefore, it is difficult to accurately estimate the oxygen concentration in the oxide semiconductor film using a method such as SIMS (Secondary Ion Mass Spectrometry). That is, it can be said that it is difficult to determine whether oxygen is intentionally added to the oxide semiconductor film.

By the way, it is known that oxygen has isotopes such as ¹⁷ O and ¹⁸ O, and their abundance ratios in the natural world are about 0.037% and 0.204% of the whole oxygen atom, respectively. In other words, since the concentration of these isotopes in the oxide semiconductor film can be estimated by a method such as SIMS, the oxygen concentration in the oxide semiconductor film can be more accurately measured by measuring these concentrations. It may be possible to estimate. Therefore, it may be determined whether oxygen is intentionally added to the oxide semiconductor film by measuring these concentrations.

In the case where oxygen 431 is directly introduced into the amorphous oxide semiconductor film 441 as in this embodiment, an insulating film (a gate insulating film 402, an insulating film 407, or the like) in contact with the amorphous oxide semiconductor film 441 is formed. Although not necessarily a film containing a large amount of oxygen, an insulating film (a gate insulating film 402, an insulating film 407, or the like) in contact with the amorphous oxide semiconductor film 441 is a film containing a large amount of oxygen, and oxygen 431 is further added. A plurality of oxygen supply methods may be performed by directly introducing the oxide film into the amorphous oxide semiconductor film 441.

Next, the amorphous oxide semiconductor film 441 is processed into an island-shaped amorphous oxide semiconductor film 443 by a second photolithography process (see FIG. 1C). Further, a resist mask for forming the island-shaped amorphous oxide semiconductor film 443 may be formed by an inkjet method. When the resist mask is formed by an ink-jet method, a manufacturing cost can be reduced because a photomask is not used.

Note that in one embodiment of the disclosed invention, an oxide semiconductor film (an amorphous oxide semiconductor film and a crystalline oxide semiconductor film) may be processed into an island shape as described in this embodiment, The shape may be left as it is without being processed.

In the case where a contact hole is formed in the gate insulating film 402, the process can be performed at the same time as the processing of the amorphous oxide semiconductor film 443.

Note that etching of the amorphous oxide semiconductor film 441 here may be dry etching or wet etching, or both of them may be used. For example, as an etchant used for wet etching of the amorphous oxide semiconductor film 441, a mixed solution of phosphoric acid, acetic acid, and nitric acid, or the like can be used. In addition, ITO07N (manufactured by Kanto Chemical Co., Inc.) may be used.

Next, a conductive film to be a source electrode layer and a drain electrode layer (including a wiring formed using the same layer) is formed over the gate insulating film 402 and the amorphous oxide semiconductor film 443. The conductive film is formed using a material that can withstand heat treatment performed later. As the conductive film used for the source electrode layer and the drain electrode layer, for example, a metal film containing an element selected from Al, Cr, Cu, Ta, Ti, Mo, and W, or metal nitriding containing the above-described element as a component A material film (titanium nitride film, molybdenum nitride film, tungsten nitride film) or the like can be used. Further, a refractory metal film such as Ti, Mo, W or the like or a metal nitride film thereof (titanium nitride film, molybdenum nitride film, tungsten nitride film) is provided on one or both of the lower side or the upper side of a metal film such as Al or Cu. It is good also as a structure which laminated | stacked. The conductive film used for the source electrode layer and the drain electrode layer may be formed using a conductive metal oxide. Examples of the conductive metal oxide include indium oxide (In ₂ O ₃ ), tin oxide (SnO ₂ ), zinc oxide (ZnO), indium tin oxide (In ₂ O ₃ —SnO ₂ ), and indium zinc oxide (In ₂ O ₃ —ZnO) or a metal oxide material containing silicon oxide can be used.

A resist mask is formed over the conductive film by a third photolithography step, and selective etching is performed to form the source electrode layer 405a and the drain electrode layer 405b, and then the resist mask is removed.

In order to reduce the number of photomasks used in the photolithography process and the number of processes, the etching process may be performed using a resist mask formed by a multi-tone mask that is an exposure mask in which transmitted light has a plurality of intensities. Good. A resist mask formed using a multi-tone mask has a shape with a plurality of thicknesses, and the shape can be further deformed by etching. Therefore, the resist mask can be used for a plurality of etching processes for processing into different patterns. . Therefore, a resist mask corresponding to at least two kinds of different patterns can be formed by using one multi-tone mask. Therefore, the number of exposure masks can be reduced, and the corresponding photolithography process can be reduced, so that the process can be simplified.

Note that it is preferable that etching conditions be optimized so as not to etch and divide the amorphous oxide semiconductor film 443 when the conductive film is etched. However, it is difficult to obtain a condition that only the conductive film is etched and the amorphous oxide semiconductor film 443 is not etched at all. Only part of the amorphous oxide semiconductor film 443 is etched when the conductive film is etched. In some cases, the oxide semiconductor film has a groove (concave portion).

In this embodiment, a Ti film is used as the conductive film and an In—Ga—Zn-based oxide semiconductor is used for the amorphous oxide semiconductor film 443; therefore, ammonia overwater (ammonia, water, excess A mixed solution of hydrogen oxide water).

Next, an insulating film 407 in contact with part of the amorphous oxide semiconductor film 443 is formed (see FIG. 1D). The insulating film 407 may be a single layer or a stacked layer, but has a structure including an aluminum oxide film.

The thickness of the aluminum oxide film included in the insulating film 407 is 30 nm to 500 nm, preferably 50 nm to 200 nm. The insulating film 407 can be formed as appropriate by a method such as sputtering, in which an impurity such as water or hydrogen is not mixed into the insulating film 407. When hydrogen is contained in the insulating film 407, penetration of the hydrogen into the oxide semiconductor film or extraction of oxygen in the oxide semiconductor film due to hydrogen occurs, so that the back channel of the oxide semiconductor film has low resistance (N-type reduction). And a parasitic channel may be formed. Therefore, it is important not to use hydrogen in the deposition method so that the insulating film 407 contains as little hydrogen as possible.

The aluminum oxide film also preferably includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio in the crystalline state of the aluminum oxide. In this case, the oxygen content is set to exceed the stoichiometric composition ratio of aluminum oxide. Alternatively, the oxygen content is set to exceed the amount of oxygen in the case of a single crystal. Oxygen may be present between the aluminum oxide lattices. When the composition is expressed by AlO _x (x> 0), it is preferable to use an aluminum oxide film having an oxygen excess region where x exceeds 3/2. Such an oxygen-excess region may be present in a part (including the interface) of the aluminum oxide film.

In this embodiment, an aluminum oxide film with a thickness of 100 nm is formed as the insulating film 407 by a sputtering method. The aluminum oxide film can be formed by a sputtering method in a rare gas (typically argon) atmosphere, an oxygen atmosphere, or a mixed atmosphere of a rare gas and oxygen.

In the same manner as in the formation of the oxide semiconductor film, an adsorption vacuum pump (such as a cryopump) is preferably used in order to remove residual moisture in the deposition chamber of the insulating film 407. The concentration of impurities contained in the insulating film 407 formed in the deposition chamber evacuated using a cryopump can be reduced. Further, as an evacuation unit for removing moisture remaining in the deposition chamber of the insulating film 407, a turbo molecular pump provided with a cold trap may be used.

As a sputtering gas used for forming the insulating film 407, a high-purity gas from which impurities such as hydrogen, water, a hydroxyl group, or hydride are removed is preferably used.

In the case where the insulating film 407 is stacked, an inorganic insulating film such as a silicon oxide film, a silicon oxynitride film, an aluminum oxynitride film, or a gallium oxide film can be typically used in addition to the aluminum oxide film. FIG. 10A illustrates an example of a transistor 410a in the transistor 410 in which the insulating film 407 has a stacked structure of the insulating film 407a and the insulating film 407b.

As shown in FIG. 10 (A), the crystalline oxide semiconductor film 403, and form the source electrode layer 405a, the insulating film 407 b on the drain electrode layer 405 b, an insulating film 407 a on the insulating film 407 b . As the insulating film 407 b , an oxide insulating film including a region with an excessive oxygen content is preferably used because it serves as a supply source of oxygen to the crystalline oxide semiconductor film 403. For example, in this embodiment, as the insulating film 407 b, compared to a stoichiometric composition ratio silicon oxide in a crystalline state, using a silicon oxide film in which the content of oxygen is contained excessive region, the insulating film an aluminum oxide film is used as the 407 a.

Next, heat treatment is performed on the amorphous oxide semiconductor film 443 so that at least part of the amorphous oxide semiconductor film 443 is crystallized, so that a crystalline oxide semiconductor film 403 including crystals is formed. In this embodiment, the crystalline oxide semiconductor film 403 includes a crystal having a c-axis substantially perpendicular to the surface.

The aluminum oxide film provided as the insulating film 407 over the amorphous oxide semiconductor film 443 has a high blocking effect (blocking effect) that prevents the film from passing through both impurities such as hydrogen and moisture and oxygen.

Therefore, the aluminum oxide film is formed into an oxide semiconductor film (amorphous oxide semiconductor film 443 and crystalline oxide semiconductor film 403) of impurities such as hydrogen and moisture which are factors of variation during and after the manufacturing process. It functions as a protective film for preventing entry and release of oxygen which is a main component material of the oxide semiconductor from the oxide semiconductor film (the amorphous oxide semiconductor film 443 and the crystalline oxide semiconductor film 403).

Since heat treatment for crystallizing the amorphous oxide semiconductor film 443 is performed in a state where the amorphous oxide semiconductor film 443 is covered with an aluminum oxide film provided as the insulating film 407, heating for crystallization is performed. By the treatment, release of oxygen from the amorphous oxide semiconductor film 443 can be prevented. Therefore, the obtained crystalline oxide semiconductor film 403 maintains the amount of oxygen contained in the amorphous oxide semiconductor film 443, and the content of oxygen is higher than the stoichiometric composition ratio of the oxide semiconductor in a crystalline state. A film including an excessive region can be obtained.

In the crystalline oxide semiconductor film 403, oxygen vacancies exist at locations where oxygen is released. An oxide semiconductor that does not contain excess oxygen cannot be supplemented with other oxygen even if oxygen vacancies occur. However, the crystalline oxide semiconductor film 403 according to one embodiment of the disclosed invention includes a crystalline oxide semiconductor film containing excess oxygen (in this embodiment, a crystal having a c-axis substantially perpendicular to the surface). A crystalline oxide semiconductor film 403 contains excess oxygen (preferably oxygen in excess of the stoichiometric composition ratio) even if oxygen vacancies occur. By containing, the excess oxygen acts on the deficient portion, and oxygen can be immediately compensated in the deficient portion.

Therefore, when the crystalline oxide semiconductor film 403 is used for the transistor 410, variation in the threshold voltage Vth of the transistor 410 and shift in threshold voltage ΔVth due to oxygen vacancies can be reduced.

The temperature of heat treatment for crystallizing at least part of the amorphous oxide semiconductor film 443 is 250 ° C. or higher and 700 ° C. or lower, preferably 400 ° C. or higher, more preferably 500 ° C., and further preferably 550 ° C. or higher.

For example, a substrate is introduced into an electric furnace which is one of heat treatment apparatuses, and the oxide semiconductor film is subjected to heat treatment at 450 ° C. for 1 hour in an oxygen atmosphere.

Note that the heat treatment apparatus is not limited to an electric furnace, and an apparatus for heating an object to be processed by heat conduction or heat radiation from a heating element such as a resistance heating element may be used. For example, a rapid thermal annealing (RTA) device such as a GRTA (Gas Rapid Thermal Anneal) device or an LRTA (Lamp Rapid Thermal Anneal) device can be used. The LRTA apparatus is an apparatus that heats an object to be processed by radiation of light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high pressure sodium lamp, or a high pressure mercury lamp. The GRTA apparatus is an apparatus that performs heat treatment using a high-temperature gas. As the high-temperature gas, an inert gas that does not react with an object to be processed by heat treatment, such as nitrogen or a rare gas such as argon, is used.

For example, as the heat treatment, GRTA may be performed in which the substrate is placed in an inert gas heated to a high temperature of 650 ° C. to 700 ° C., heated for several minutes, and then the substrate is taken out of the inert gas.

Note that as the heat treatment for crystallization, heat treatment by light irradiation with laser light, lamp light, or the like may be used. For example, the amorphous oxide semiconductor film can be crystallized by irradiation with laser light having a wavelength that is absorbed by the amorphous oxide semiconductor film.

The heat treatment may be performed in an atmosphere of nitrogen, oxygen, ultra-dry air (air with a water content of 20 ppm or less, preferably 1 ppm or less, preferably 10 ppb or less), or a rare gas (such as argon or helium). It is preferable that water, hydrogen, etc. are not contained in the atmosphere of nitrogen, oxygen, ultra-dry air, or rare gas. Further, the purity of nitrogen, oxygen, or a rare gas introduced into the heat treatment apparatus is 6N (99.9999%) or more, preferably 7N (99.99999%) or more (that is, the impurity concentration is 1 ppm or less, preferably 0.1 ppm). Or less).

In the crystalline oxide semiconductor film 403 which is highly purified and in which oxygen vacancies are filled, impurities such as hydrogen and water are sufficiently removed, and the hydrogen concentration in the crystalline oxide semiconductor film 403 is 5 × 10 ^19. / Cm ³ or less, preferably 5 × 10 ¹⁸ / cm ³ or less. Note that the hydrogen concentration in the crystalline oxide semiconductor film 403 is measured by secondary ion mass spectrometry (SIMS).

Such a crystalline oxide semiconductor film 403 has very few carriers (close to zero), and the carrier concentration is less than 1 × 10 ¹⁴ / cm ³ , preferably less than 1 × 10 ¹² / cm ³ , and more preferably 1 It is less than × 10 ¹¹ / cm ³ .

Through the above process, the transistor 410 is formed (see FIG. 1E). The transistor 410 is a transistor including a crystalline oxide semiconductor film which is highly purified and contains excess oxygen which fills oxygen vacancies. Thus, the transistor 410 has stable electrical characteristics and is electrically stable.

A transistor 410 using the crystalline oxide semiconductor film 403 which is manufactured using this embodiment and includes oxygen which is highly purified and fills oxygen vacancies excessively has an off-state current value (off-state current value) as follows: 100 zA / μm (1 zA (zeptoampere) is 1 × 10 ⁻²¹ A) or less, preferably 10 zA / μm or less, more preferably 1 zA / μm or less, more preferably 100 yA / μm or less at room temperature per channel width of 1 μm. Can be lowered.

As described above, a semiconductor device including an oxide semiconductor having stable electrical characteristics can be provided. Therefore, a highly reliable semiconductor device can be provided.

This embodiment can be implemented in appropriate combination with any of the other embodiments.

(Embodiment 2)
In this embodiment, another embodiment of a semiconductor device and a method for manufacturing the semiconductor device will be described with reference to FIGS. The same portions as those in the above embodiment or portions and processes having similar functions can be performed in the same manner as in the above embodiment, and repeated description is omitted. Detailed descriptions of the same parts are omitted.

In this embodiment, an example in which the oxygen introduction step into the amorphous oxide semiconductor film is performed through the insulating film provided over the transistor 410 in the method for manufacturing a semiconductor device according to the disclosed invention.

2A to 2E illustrate an example of a method for manufacturing the transistor 410 in this embodiment.

After a conductive film is formed over the substrate 400 having an insulating surface, a gate electrode layer 401 is formed.

Next, the gate insulating film 402 is formed over the gate electrode layer 401 by a plasma CVD method, a sputtering method, or the like.

Next, an amorphous oxide semiconductor film 491 with a thickness of 2 nm to 200 nm, preferably 5 nm to 30 nm is formed over the gate insulating film 402 (see FIG. 2A).

Further, heat treatment for removing (dehydrating or dehydrogenating) excess hydrogen (including water and a hydroxyl group) may be performed on the amorphous oxide semiconductor film 491.

Next, the amorphous oxide semiconductor film 491 is processed into an island-shaped amorphous oxide semiconductor film 492 by a photolithography process (see FIG. 2B).

Next, the source electrode layer 405 a and the drain electrode layer 405 b are formed over the gate insulating film 402 and the amorphous oxide semiconductor film 492.

Next, an insulating film 407 in contact with part of the amorphous oxide semiconductor film 492 is formed (see FIG. 2C). The insulating film 407 may be a single layer or a stacked layer, but has a structure including an aluminum oxide film.

In this embodiment, an aluminum oxide film with a thickness of 100 nm is formed as the insulating film 407 by a sputtering method.

Next, oxygen 431 (including at least one of oxygen radicals, oxygen atoms, and oxygen ions) is introduced into the amorphous oxide semiconductor film 492 so that oxygen is supplied to the amorphous oxide semiconductor film 492. Do.

In this embodiment, after the insulating film 407 is formed, oxygen 431 is implanted into the amorphous oxide semiconductor film 492 through the insulating film 407 by an ion implantation method. Through the implantation process of oxygen 431, the amorphous oxide semiconductor film 492 is formed into an amorphous oxide film in which an oxide semiconductor includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio in a crystalline state. The semiconductor film 443 is formed (see FIG. 2D).

Oxygen vacancies existing in the amorphous oxide semiconductor film 443 can be filled with the supplied oxygen 431.

Note that depending on oxygen introduction conditions, oxygen may be introduced into part of the insulating film (and the insulating film and the amorphous oxide semiconductor film) when oxygen is introduced into the amorphous oxide semiconductor film through the insulating film. It is also possible to introduce it to the interface). For example, in the case where the insulating film has a stacked structure of an oxide insulating film (eg, a silicon oxide film) and an aluminum oxide film, the amorphous oxide semiconductor film is in contact with oxygen when it is introduced into the amorphous oxide semiconductor film. Oxygen is also introduced into the interface between the oxide insulating film, the amorphous oxide semiconductor film, and the oxide insulating film, and an oxygen-excess region is formed in the stack of the amorphous oxide semiconductor film and the oxide insulating film. can do.

Next, the amorphous oxide semiconductor film 443 is subjected to heat treatment, and at least part of the amorphous oxide semiconductor film 443 is crystallized, so that the crystalline oxide semiconductor film 403 is formed.

In this embodiment, as the crystalline oxide semiconductor film 403, a crystalline oxide semiconductor film 403 including a crystal having a c-axis substantially perpendicular to the surface is formed.

The aluminum oxide film provided as the insulating film 407 over the amorphous oxide semiconductor film 443 has a high blocking effect (blocking effect) that prevents the film from passing through both impurities such as hydrogen and moisture and oxygen.

Therefore, the aluminum oxide film is formed into an oxide semiconductor film (amorphous oxide semiconductor film 443 and crystalline oxide semiconductor film 403) of impurities such as hydrogen and moisture which are factors of variation during and after the manufacturing process. It functions as a protective film for preventing entry and release of oxygen which is a main component material of the oxide semiconductor from the oxide semiconductor film (the amorphous oxide semiconductor film 443 and the crystalline oxide semiconductor film 403).

Since heat treatment for crystallizing the amorphous oxide semiconductor film 443 is performed in a state where the amorphous oxide semiconductor film 443 is covered with an aluminum oxide film provided as the insulating film 407, heating for crystallization is performed. By the treatment, release of oxygen from the amorphous oxide semiconductor film 443 can be prevented. Therefore, the obtained crystalline oxide semiconductor film 403 maintains the amount of oxygen contained in the amorphous oxide semiconductor film 443, and the oxide semiconductor has an oxygen content with respect to the stoichiometric composition ratio in the crystalline state. A film including an excessive region can be obtained.

Accordingly, the formed crystalline oxide semiconductor film 403 has high purity because entry of impurities such as hydrogen and moisture and release of excessively introduced oxygen are prevented by the aluminum oxide film. Includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio in the crystalline state.

In the crystalline oxide semiconductor film 403, oxygen vacancies exist at locations where oxygen is released. An oxide semiconductor that does not contain excess oxygen cannot be supplemented with other oxygen even if oxygen vacancies occur. However, the crystalline oxide semiconductor film 403 according to one embodiment of the disclosed invention is a film containing excess oxygen (in this embodiment, a CAAC-OS film containing excess oxygen), and the crystalline oxide semiconductor film Even if oxygen vacancies occur, 403 contains excess oxygen (preferably oxygen in excess of the stoichiometric composition ratio) in the film. Can be filled in the missing part.

Through the above steps, the transistor 410 is formed (see FIG. 2E). The transistor 410 is a transistor including a crystalline oxide semiconductor film which is highly purified and contains excess oxygen which fills oxygen vacancies. Thus, the transistor 410 has stable electrical characteristics and is electrically stable.

As described above, a semiconductor device including an oxide semiconductor having stable electrical characteristics can be provided. Therefore, a highly reliable semiconductor device can be provided.

This embodiment can be implemented in appropriate combination with any of the other embodiments.

(Embodiment 3)
In this embodiment, another embodiment of a semiconductor device and a method for manufacturing the semiconductor device will be described with reference to FIGS. The same portions as those in the above embodiment or portions and processes having similar functions can be performed in the same manner as in the above embodiment, and repeated description is omitted. Detailed descriptions of the same parts are omitted.

A transistor 430 illustrated in FIGS. 3A to 3E is an example of a bottom-gate transistor.

The transistor 430 includes a gate electrode layer 401, a gate insulating film 402, a source electrode layer 405a, a drain electrode layer 405b, and a crystalline oxide semiconductor film 403 over a substrate 400 having an insulating surface. In addition, an insulating film 407 is formed to cover the transistor 430.

3A to 3E illustrate an example of a method for manufacturing the transistor 430.

First, the gate electrode layer 401 is formed over the substrate 400 having an insulating surface (see FIG. 3A).

A gate insulating film 402 is formed over the gate electrode layer 401. In this embodiment, a silicon oxide film is used for the gate insulating film 402.

The silicon oxide film in contact with the crystalline oxide semiconductor film 403 preferably includes a region where the amount of oxygen is excessive with respect to the stoichiometric composition ratio of the silicon oxide in a crystalline state.

By setting the silicon oxide film in contact with the crystalline oxide semiconductor film 403 to a state containing a large amount of oxygen, the silicon oxide film can function suitably as a supply source for supplying oxygen to the oxide semiconductor film.

Next, a source electrode layer 405 a and a drain electrode layer 405 b are formed over the gate insulating film 402.

Next, an amorphous oxide semiconductor film is formed over the gate insulating film 402, the source electrode layer 405a, and the drain electrode layer 405b and processed into an island shape to form an amorphous oxide semiconductor film 492 (FIG. 3 (B)).

In this embodiment, as the amorphous oxide semiconductor film 492, an In—Ga—Zn-based oxide film is formed by a sputtering method using an In—Ga—Zn-based oxide target.

Further, heat treatment for removing (dehydrating or dehydrogenating) excess hydrogen (including water and a hydroxyl group) may be performed on the amorphous oxide semiconductor film 492. The temperature of the heat treatment is a temperature at which the amorphous oxide semiconductor film 492 is not crystallized, and is typically 250 ° C to 400 ° C, preferably 300 ° C.

Heat treatment for dehydration or dehydrogenation may be performed before the amorphous oxide semiconductor film 492 is processed into an island shape.

Next, oxygen 431 (including at least one of oxygen radicals, oxygen atoms, and oxygen ions) is introduced into the amorphous oxide semiconductor film 492 so that oxygen is supplied to the amorphous oxide semiconductor film 492. Do.

In this embodiment, oxygen 431 is implanted into the exposed amorphous oxide semiconductor film 492 by an ion implantation method. Through the implantation process of oxygen 431, the amorphous oxide semiconductor film 492 is formed into an amorphous oxide film in which an oxide semiconductor includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio in a crystalline state. The semiconductor film 443 is formed (see FIG. 3C).

Oxygen vacancies existing in the amorphous oxide semiconductor film 443 can be filled with the supplied oxygen 431.

Next, an insulating film 407 is formed over the amorphous oxide semiconductor film 443 (see FIG. 3D). The insulating film 407 may be a single layer or a stacked layer, but has a structure including an aluminum oxide film.

The thickness of the aluminum oxide film included in the insulating film 407 is 30 nm to 500 nm, preferably 50 nm to 200 nm.

The aluminum oxide film also preferably includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio in the crystalline state of the aluminum oxide.

In this embodiment, an aluminum oxide film with a thickness of 100 nm is formed as the insulating film 407 by a sputtering method.

Next, the amorphous oxide semiconductor film 443 is subjected to heat treatment, and at least part of the amorphous oxide semiconductor film 443 is crystallized, so that the crystalline oxide semiconductor film 403 is formed.

The temperature of heat treatment for crystallizing at least part of the amorphous oxide semiconductor film 443 is 250 ° C. or higher and 700 ° C. or lower, preferably 400 ° C. or higher, more preferably 500 ° C., and further preferably 550 ° C. or higher.

In this embodiment, as the crystalline oxide semiconductor film 403, a crystalline oxide semiconductor film 403 including a crystal having a c-axis substantially perpendicular to the surface is formed.

The aluminum oxide film provided as the insulating film 407 over the amorphous oxide semiconductor film 443 has a high blocking effect (blocking effect) that prevents the film from passing through both impurities such as hydrogen and moisture and oxygen.

Therefore, the aluminum oxide film is formed into an oxide semiconductor film (amorphous oxide semiconductor film 443 and crystalline oxide semiconductor film 403) of impurities such as hydrogen and moisture which are factors of variation during and after the manufacturing process. It functions as a protective film for preventing entry and release of oxygen which is a main component material of the oxide semiconductor from the oxide semiconductor film (the amorphous oxide semiconductor film 443 and the crystalline oxide semiconductor film 403).

Since heat treatment for crystallizing the amorphous oxide semiconductor film 443 is performed in a state where the amorphous oxide semiconductor film 443 is covered with an aluminum oxide film provided as the insulating film 407, heating for crystallization is performed. By the treatment, release of oxygen from the amorphous oxide semiconductor film 443 can be prevented. Therefore, the obtained crystalline oxide semiconductor film 403 maintains the amount of oxygen contained in the amorphous oxide semiconductor film 443, and the oxide semiconductor has an oxygen content with respect to the stoichiometric composition ratio in the crystalline state. A film including an excessive region can be obtained.

Accordingly, the formed crystalline oxide semiconductor film 403 has high purity because entry of impurities such as hydrogen and moisture and release of excessively introduced oxygen are prevented by the aluminum oxide film. Includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio in the crystalline state.

In the crystalline oxide semiconductor film 403, oxygen vacancies exist at locations where oxygen is released. An oxide semiconductor that does not contain excess oxygen cannot be supplemented with other oxygen even if oxygen vacancies occur. However, the crystalline oxide semiconductor film 403 according to one embodiment of the disclosed invention is a film containing excess oxygen (in this embodiment, a CAAC-OS film containing excess oxygen), and the crystalline oxide semiconductor film Even if oxygen vacancies occur, 403 contains excess oxygen (preferably oxygen in excess of the stoichiometric composition ratio) in the film. Can be filled in the missing part.

Therefore, when the crystalline oxide semiconductor film 403 is used for the transistor 430, variation in the threshold voltage Vth of the transistor 430 and shift in threshold voltage ΔVth due to oxygen vacancies can be reduced.

Through the above steps, the transistor 430 is formed (see FIG. 3E). The transistor 430 is a transistor having a crystalline oxide semiconductor film that is highly purified and contains oxygen in excess to fill oxygen vacancies. Thus, the transistor 430 is electrically stable because variation in electrical characteristics is suppressed.

A transistor 430 using a crystalline oxide semiconductor film 403 which is manufactured using this embodiment and includes oxygen which is highly purified and fills oxygen vacancies excessively has an off-state current value (off-state current value) as follows: 100 zA / μm (1 zA (zeptoampere) is 1 × 10 ⁻²¹ A) or less, preferably 10 zA / μm or less, more preferably 1 zA / μm or less, more preferably 100 yA / μm or less at room temperature per channel width of 1 μm. Can be lowered.

As described above, a semiconductor device including an oxide semiconductor having stable electrical characteristics can be provided. Therefore, a highly reliable semiconductor device can be provided.

This embodiment can be implemented in appropriate combination with any of the other embodiments.

(Embodiment 4)
In this embodiment, another embodiment of a semiconductor device and a method for manufacturing the semiconductor device will be described with reference to FIGS. The same portions as those in the above embodiment or portions and processes having similar functions can be performed in the same manner as in the above embodiment, and repeated description is omitted. Detailed descriptions of the same parts are omitted.

In this embodiment, an example in which the oxygen introduction step into the amorphous oxide semiconductor film is performed through the insulating film provided over the transistor 430 in the method for manufacturing a semiconductor device according to the disclosed invention.

A transistor 430 illustrated in FIGS. 4A to 4E is an example of a bottom-gate transistor. 4A to 4E illustrate an example of a method for manufacturing the transistor 430.

First, the gate electrode layer 401 is formed over the substrate 400 having an insulating surface (see FIG. 4A).

A gate insulating film 402 is formed over the gate electrode layer 401. In this embodiment, a silicon oxide film is used for the gate insulating film 402.

The silicon oxide film in contact with the crystalline oxide semiconductor film 403 preferably includes a region where the amount of oxygen is excessive with respect to the stoichiometric composition ratio of the silicon oxide in a crystalline state.

By setting the silicon oxide film in contact with the crystalline oxide semiconductor film 403 to a state containing a large amount of oxygen, the silicon oxide film can function suitably as a supply source for supplying oxygen to the oxide semiconductor film.

Next, a source electrode layer 405 a and a drain electrode layer 405 b are formed over the gate insulating film 402.

Next, an amorphous oxide semiconductor film is formed over the gate insulating film 402, the source electrode layer 405a, and the drain electrode layer 405b and processed into an island shape to form an amorphous oxide semiconductor film 492 (FIG. 4 (B)).

In this embodiment, as the amorphous oxide semiconductor film 492, an In—Ga—Zn-based oxide film is formed by a sputtering method using an In—Ga—Zn-based oxide target.

Further, heat treatment for removing (dehydrating or dehydrogenating) excess hydrogen (including water and a hydroxyl group) may be performed on the amorphous oxide semiconductor film 492. The temperature of the heat treatment is a temperature at which the amorphous oxide semiconductor film 492 is not crystallized, and is typically 250 ° C to 400 ° C, preferably 300 ° C.

Heat treatment for dehydration or dehydrogenation may be performed before the amorphous oxide semiconductor film 492 is processed into an island shape.

Next, an insulating film 407 is formed over the amorphous oxide semiconductor film 492 (see FIG. 4C). The insulating film 407 may be a single layer or a stacked layer, but has a structure including an aluminum oxide film.

The thickness of the aluminum oxide film included in the insulating film 407 is 30 nm to 500 nm, preferably 50 nm to 200 nm.

The aluminum oxide film also preferably includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio in the crystalline state of the aluminum oxide.

In this embodiment, an aluminum oxide film with a thickness of 100 nm is formed as the insulating film 407 by a sputtering method.

Next, oxygen 431 (including at least one of oxygen radicals, oxygen atoms, and oxygen ions) is introduced into the amorphous oxide semiconductor film 492 so that oxygen is supplied to the amorphous oxide semiconductor film 492. Do.

In this embodiment, after the insulating film 407 is formed, oxygen 431 is implanted into the amorphous oxide semiconductor film 492 through the insulating film 407 by an ion implantation method. Through the implantation process of oxygen 431, the amorphous oxide semiconductor film 492 is formed into an amorphous oxide film in which an oxide semiconductor includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio in a crystalline state. The semiconductor film 443 is formed (see FIG. 4D).

Oxygen vacancies existing in the amorphous oxide semiconductor film 443 can be filled with the supplied oxygen 431.

Next, the amorphous oxide semiconductor film 443 is subjected to heat treatment, and at least part of the amorphous oxide semiconductor film 443 is crystallized, so that the crystalline oxide semiconductor film 403 is formed.

The temperature of heat treatment for crystallizing at least part of the amorphous oxide semiconductor film 443 is 250 ° C. or higher and 700 ° C. or lower, preferably 400 ° C. or higher, more preferably 500 ° C., and further preferably 550 ° C. or higher.

In this embodiment, as the crystalline oxide semiconductor film 403, a crystalline oxide semiconductor film 403 including a crystal having a c-axis substantially perpendicular to the surface is formed.

The aluminum oxide film provided as the insulating film 407 over the amorphous oxide semiconductor film 443 has a high blocking effect (blocking effect) that prevents the film from passing through both impurities such as hydrogen and moisture and oxygen.

Therefore, the aluminum oxide film is formed into an oxide semiconductor film (amorphous oxide semiconductor film 443 and crystalline oxide semiconductor film 403) of impurities such as hydrogen and moisture which are factors of variation during and after the manufacturing process. It functions as a protective film for preventing entry and release of oxygen which is a main component material of the oxide semiconductor from the oxide semiconductor film (the amorphous oxide semiconductor film 443 and the crystalline oxide semiconductor film 403).

Since heat treatment for crystallizing the amorphous oxide semiconductor film 443 is performed in a state where the amorphous oxide semiconductor film 443 is covered with an aluminum oxide film provided as the insulating film 407, heating for crystallization is performed. By the treatment, release of oxygen from the amorphous oxide semiconductor film 443 can be prevented. Therefore, the obtained crystalline oxide semiconductor film 403 maintains the amount of oxygen contained in the amorphous oxide semiconductor film 443, and the oxide semiconductor has an oxygen content with respect to the stoichiometric composition ratio in the crystalline state. A film including an excessive region can be obtained.

Accordingly, the formed crystalline oxide semiconductor film 403 has high purity because entry of impurities such as hydrogen and moisture and release of excessively introduced oxygen are prevented by the aluminum oxide film. Includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio in the crystalline state.

In the crystalline oxide semiconductor film 403, oxygen vacancies exist at locations where oxygen is released. An oxide semiconductor that does not contain excess oxygen cannot be supplemented with other oxygen even if oxygen vacancies occur. However, the crystalline oxide semiconductor film 403 according to one embodiment of the disclosed invention is a film containing excess oxygen (in this embodiment, a CAAC-OS film containing excess oxygen), and the crystalline oxide semiconductor film Even if oxygen vacancies occur, 403 contains excess oxygen (preferably oxygen in excess of the stoichiometric composition ratio) in the film. Can be filled in the missing part.

Through the above steps, the transistor 430 is formed (see FIG. 4E). The transistor 430 is a transistor having a crystalline oxide semiconductor film that is highly purified and contains oxygen in excess to fill oxygen vacancies. Thus, the transistor 430 is electrically stable because variation in electrical characteristics is suppressed.

As described above, a semiconductor device including an oxide semiconductor having stable electrical characteristics can be provided. Therefore, a highly reliable semiconductor device can be provided.

This embodiment can be implemented in appropriate combination with any of the other embodiments.

(Embodiment 5)
In this embodiment, one embodiment of a semiconductor device and a method for manufacturing the semiconductor device will be described with reference to FIGS. In this embodiment, a transistor including an oxide semiconductor film is described as an example of a semiconductor device. The same portions as those in the above embodiment or portions and processes having similar functions can be performed in the same manner as in the above embodiment, and repeated description is omitted. Detailed descriptions of the same parts are omitted.

A transistor 440 illustrated in FIGS. 5A to 5F is an example of a top-gate transistor.

As shown in FIG. 5F, a transistor 440 includes a source electrode layer 405a, a drain electrode layer 405b, a crystalline oxide semiconductor film 403, a gate insulating film over a substrate 400 having an insulating surface provided with an insulating film 436. A film 402 and a gate electrode layer 401 are included. An insulating film 407 is formed over the transistor 440.

The insulating film 407 may be a single layer or a stacked layer, but has a structure including an aluminum oxide film. In this embodiment, an aluminum oxide film is used as the insulating film 407.

The crystalline oxide semiconductor film 403 is an oxide semiconductor film having crystallinity. In this embodiment, the crystalline oxide semiconductor film 403 has an ab plane parallel to the surface and is substantially perpendicular to the surface. A crystalline oxide semiconductor (CAAC-OS) having a c-axis orientation and having a structure which is neither a single crystal structure nor an amorphous structure . By using a crystalline oxide semiconductor film, a change in electrical characteristics of the transistor due to irradiation with visible light or ultraviolet light can be further suppressed, and a highly reliable semiconductor device can be obtained.

5A to 5F illustrate an example of a method for manufacturing the transistor 440. FIG.

First, the insulating film 436 is formed over the substrate 400 having an insulating surface.

As the insulating film 436, silicon oxide, silicon oxynitride, aluminum oxide, aluminum oxynitride, hafnium oxide, gallium oxide, silicon nitride, silicon nitride oxide, aluminum nitride, aluminum nitride oxide, or the like is formed by a plasma CVD method, a sputtering method, or the like. It can be formed using these mixed materials.

Although the insulating film 436 may be a single layer or a stacked layer, an oxide insulating film is preferably used as a film in contact with the crystalline oxide semiconductor film 403. In this embodiment, a silicon oxide film formed by a sputtering method is used as the insulating film 436.

Next, an amorphous oxide semiconductor film 491 is formed over the insulating film 436 (see FIG. 5A).

Since the insulating film 436 is in contact with the amorphous oxide semiconductor film 491, it is preferable that oxygen in an amount exceeding at least the stoichiometric composition ratio exists in the film (in the bulk). For example, when a silicon oxide film is used as the insulating film 436, SiO _{2 + α} (α> 0) is set. By using such an insulating film 436, oxygen can be supplied to the amorphous oxide semiconductor film 491, so that characteristics can be improved. By supplying oxygen to the amorphous oxide semiconductor film 491, oxygen vacancies in the film can be filled.

For example, by providing the insulating film 436 containing a large amount (excess) of oxygen serving as an oxygen supply source in contact with the amorphous oxide semiconductor film 491, oxygen can be transferred from the insulating film 436 to the amorphous oxide semiconductor film 491. Can be supplied. Oxygen may be supplied to the crystalline oxide semiconductor film 403 by performing a heating step with the amorphous oxide semiconductor film 491 and the insulating film 436 in contact with each other.

In the insulating film 436, a region where the crystalline oxide semiconductor film 403 (the amorphous oxide semiconductor film 491 in the process of FIG. 5A) is in contact is a surface with reduced surface roughness. Preferably there is. Specifically, the average surface roughness of the surface is 1 nm or less, preferably 0.3 nm or less, more preferably 0.1 nm or less. By forming the crystalline oxide semiconductor film 403 (the amorphous oxide semiconductor film 491 in the process of FIG. 5A) on the surface with reduced surface roughness, crystallinity having stable and favorable crystallinity is obtained. The oxide semiconductor film 403 can be obtained.

Therefore, planarization treatment may be performed on a region in the insulating film 436 where the crystalline oxide semiconductor film 403 (the amorphous oxide semiconductor film 491 in the process of FIG. 5A) is in contact with the insulating film 436. The planarization treatment is not particularly limited, and polishing treatment (for example, chemical mechanical polishing (CMP) method), dry etching treatment, or plasma treatment can be used.

As the plasma treatment, for example, reverse sputtering in which an argon gas is introduced to generate plasma can be performed. Inverse sputtering is a method in which a surface is modified by forming a plasma near the substrate by applying a voltage to the substrate side using an RF power source in an argon atmosphere. Note that nitrogen, helium, oxygen, or the like may be used instead of the argon atmosphere. When reverse sputtering is performed, powdery substances (also referred to as particles or dust) attached to the surface of the insulating film 436 can be removed.

As the planarization treatment, the polishing treatment, the dry etching treatment, and the plasma treatment may be performed a plurality of times or in combination. Further, in the case of performing the combination, the order of steps is not particularly limited, and may be set as appropriate in accordance with the uneven state of the surface of the insulating film 436.

In the step of forming the amorphous oxide semiconductor film 491, in order to prevent the amorphous oxide semiconductor film 491 from containing hydrogen or water as much as possible, before the amorphous oxide semiconductor film 491 is formed, As the treatment, it is preferable that the substrate over which the insulating film 436 is formed be preheated in the preheating chamber of the sputtering apparatus, and impurities such as hydrogen and moisture adsorbed on the substrate and the insulating film 436 are desorbed and exhausted. Note that a cryopump is preferable as an exhaustion unit provided in the preheating chamber.

The thickness of the amorphous oxide semiconductor film 491 is 1 nm to 200 nm (preferably 5 nm to 30 nm). Deposition) method or the like can be used as appropriate.

Further, the amorphous oxide semiconductor film 491 may be subjected to heat treatment for removing (dehydrating or dehydrogenating) excess hydrogen (including water and a hydroxyl group). The temperature of the heat treatment is a temperature at which the amorphous oxide semiconductor film is not crystallized, and is typically 250 ° C to 400 ° C, preferably 300 ° C.

The heat treatment can be performed under reduced pressure or a nitrogen atmosphere. For example, the substrate is introduced into an electric furnace which is one of heat treatment apparatuses, and the oxide semiconductor film is subjected to a heating process at 450 ° C. for 1 hour in a nitrogen atmosphere. After the amorphous oxide semiconductor film 491 is heated by heat treatment, high-purity oxygen gas, high-purity oxygen dinitride gas, or ultra-dry air may be introduced into the same furnace. Oxygen, which is a main component material of an amorphous oxide semiconductor that has been simultaneously reduced by an impurity removal step by dehydration or dehydrogenation treatment by the action of oxygen gas or oxygen dinitride gas, can be supplied. it can.

When the heating step for dehydration or dehydrogenation is performed before the amorphous oxide semiconductor film 491 is processed into an island shape into the amorphous oxide semiconductor film 492, oxygen contained in the insulating film 436 is removed. It is preferable because it can be prevented from being released by the heating step.

Note that the amorphous oxide semiconductor film 491 may be processed into an island shape, or may be left in a film shape without being processed. In addition, an element isolation region including an insulating film for isolating the amorphous oxide semiconductor film 491 for each element may be provided.

In this embodiment, the amorphous oxide semiconductor film 491 is processed into an island-shaped amorphous oxide semiconductor film 492 by a photolithography process.

Note that the amorphous oxide semiconductor film 491 may be etched by dry etching or wet etching, or both. For example, as an etchant used for wet etching of the amorphous oxide semiconductor film 491, a mixed solution of phosphoric acid, acetic acid, and nitric acid, or the like can be used. In addition, ITO07N (manufactured by Kanto Chemical Co., Inc.) may be used.

Next, a gate insulating film 442 which covers the amorphous oxide semiconductor film 492 is formed (see FIG. 5B).

Note that the planarization treatment may be performed on the surface of the amorphous oxide semiconductor film 492 in order to improve the coverage with the gate insulating film 442 formed over the amorphous oxide semiconductor film 492. In particular, when a thin insulating film is used as the gate insulating film 442, it is preferable that the surface of the amorphous oxide semiconductor film 492 be flat.

The thickness of the gate insulating film 442 is 1 nm to 100 nm, and a sputtering method, an MBE method, a CVD method, a pulse laser deposition method, an ALD method, or the like can be used as appropriate. Alternatively, the gate insulating film 442 may be formed using a sputtering apparatus that performs film formation in a state where a plurality of substrate surfaces are set substantially perpendicular to the surface of the sputtering target, that is, a so-called CP sputtering apparatus.

As a material of the gate insulating film 442, a silicon oxide film, a gallium oxide film, an aluminum oxide film, a silicon nitride film, a silicon oxynitride film, an aluminum oxynitride film, or a silicon nitride oxide film can be used. The gate insulating film 442 preferably contains oxygen in a portion in contact with the amorphous oxide semiconductor film 492. In particular, the gate insulating film 442 preferably includes oxygen in the film (in the bulk) in an amount exceeding at least the stoichiometric composition ratio. For example, when a silicon oxide film is used as the gate insulating film 442, , SiO _{2 + α} (where α> 0). In this embodiment, a silicon oxide film of SiO _{2 + α} (α> 0) is used as the gate insulating film 442. By using this silicon oxide film as the gate insulating film 442, oxygen can be supplied to the amorphous oxide semiconductor film 492, so that characteristics can be improved. Further, the gate insulating film 442 is preferably formed in consideration of the size of a transistor to be manufactured and the step coverage of the gate insulating film 442.

Further, as a material of the gate insulating film 442, hafnium oxide, yttrium oxide, hafnium silicate (HfSi _x O _y (x> 0, y> 0)), hafnium silicate to which nitrogen is added (HfSiO _x N _y (x> 0, The gate leakage current can be reduced by using a high-k material such as y> 0)), hafnium aluminate (HfAl _x O _y (x> 0, y> 0)), or lanthanum oxide. Further, the gate insulating film 442 may have a single-layer structure or a stacked structure.

Next, oxygen 431 (including at least one of oxygen radicals, oxygen atoms, and oxygen ions) is introduced into the amorphous oxide semiconductor film 492 so that oxygen is supplied to the amorphous oxide semiconductor film 492. Do. As a method for introducing oxygen, an ion implantation method, an ion doping method, a plasma immersion ion implantation method, a plasma treatment, or the like can be used.

In the manufacturing process of the transistor 440 in this embodiment, the oxygen introduction step is performed after the amorphous oxide semiconductor film 491 is formed and before the aluminum oxide film is formed as the insulating film 407. Note that heat treatment for dehydration or dehydrogenation is performed before the oxygen introduction step. The oxygen introduction step may be directly introduced into the amorphous oxide semiconductor film, or may be introduced into the amorphous oxide semiconductor film through another film such as a gate insulating film or an insulating film. Also good. When oxygen is introduced into an amorphous oxide semiconductor film through another film, an ion implantation method, an ion doping method, a plasma immersion ion implantation method, or the like may be used. In the case of directly introducing the oxide semiconductor film (for example, after the amorphous oxide semiconductor film 491 is formed and after the amorphous oxide semiconductor film 492 is formed), plasma treatment or the like can also be used.

In this embodiment, oxygen 431 is implanted into the amorphous oxide semiconductor film 492 through the gate insulating film 442 by an ion implantation method. Through the implantation process of oxygen 431, an amorphous oxide semiconductor film 443 including a region where the oxygen content is excessive with respect to the stoichiometric composition ratio of the oxide semiconductor in a crystalline state is obtained (FIG. 5 ( C)).

Note that the amorphous state in the amorphous oxide semiconductor film 443 can be made more uniform by the step of introducing oxygen 431.

For example, the oxygen concentration in the amorphous oxide semiconductor film 443 introduced by the step of introducing oxygen 431 is preferably 1 × 10 ¹⁸ / cm ³ or more and 3 × 10 ²¹ / cm ³ or less. Note that the oxygen-excess region only needs to exist in part (including the interface) of the amorphous oxide semiconductor film 443. Therefore, by introducing oxygen 431, the interface between the insulating film 436 and the amorphous oxide semiconductor film 443, the amorphous oxide semiconductor film 443, or the amorphous oxide semiconductor film 443 and the gate insulating film 442 are introduced. Oxygen is contained in at least one of the interfaces.

The amorphous oxide semiconductor film 443 includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio of the oxide semiconductor in a crystalline state. In this case, the oxygen content is set to exceed the stoichiometric composition ratio of the oxide semiconductor. Alternatively, the oxygen content is set to exceed the amount of oxygen in the case of a single crystal. Oxygen may exist between lattices of the oxide semiconductor. The composition of such an oxide semiconductor can be represented by InGaZn _m O _{m + 3x} (x> 1). For example, when m = 1, the composition of the oxide semiconductor is InGaZnO _{1 + 3x} (x> 1). When oxygen is excessive, 1 + 3x exceeds 4.

Oxygen vacancies existing in the amorphous oxide semiconductor film 443 can be filled with the supplied oxygen 431.

In the case where oxygen is directly introduced into an amorphous oxide semiconductor film as in this embodiment, the insulating film in contact with the amorphous oxide semiconductor film is not necessarily a film containing a large amount of oxygen. The insulating film in contact with the amorphous oxide semiconductor film may be a film containing much oxygen, and oxygen may be directly introduced into the amorphous oxide semiconductor film to perform a plurality of oxygen supply methods.

Then, the gate electrode layer 401 is formed over the gate insulating film 442. The material of the gate electrode layer 401 can be formed using a metal material such as molybdenum, titanium, tantalum, tungsten, aluminum, copper, chromium, neodymium, or scandium, or an alloy material containing any of these materials as its main component. As the gate electrode layer 401, a semiconductor film typified by a polycrystalline silicon film doped with an impurity element such as phosphorus, or a silicide film such as nickel silicide may be used. The gate electrode layer 401 may have a single-layer structure or a stacked structure.

The material of the gate electrode layer 401 is indium tin oxide, indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, indium A conductive material such as zinc oxide or indium tin oxide to which silicon oxide is added can also be used. Alternatively, a stacked structure of the conductive material and the metal material can be employed.

Further, as one layer of the gate electrode layer 401 in contact with the gate insulating film 442, a metal oxide containing nitrogen, specifically, an In—Ga—Zn—O film containing nitrogen or an In—Sn—O film containing nitrogen is used. In-Ga-O films containing nitrogen, In-Zn-O films containing nitrogen, Sn-O films containing nitrogen, In-O films containing nitrogen, metal nitride films (InN, SnN, etc.) ) Can be used. These films have a work function of 5 electron volts, preferably 5.5 electron volts or more, and when used as a gate electrode layer, the threshold voltage of the electrical characteristics of the transistor can be positive. A Mary-off switching element can be realized.

Sidewall insulating layers 412 a and 412 b having a sidewall structure and a gate insulating film 402 are formed on side surfaces of the gate electrode layer 401. The sidewall insulating layers 412a and 412b are formed by forming an insulating film that covers the gate electrode layer 401, and then processing the insulating film by anisotropic etching using a RIE (Reactive Ion Etching) method to form the gate electrode. Sidewall insulating layers 412a and 412b having a sidewall structure may be formed on the side wall of the layer 401 in a self-aligning manner. Here, although there is no particular limitation on the insulating film, for example, silicon oxide having good step coverage formed by reacting TEOS (tetraethyl-ortho-silicate) or silane with oxygen or nitrous oxide is used. Can do. The insulating film can be formed by a method such as thermal CVD, plasma CVD, atmospheric pressure CVD, bias ECRCVD, or sputtering. Alternatively, silicon oxide formed by a low temperature oxidation (LTO) method may be used.

The gate insulating film 402 can be formed by etching the gate insulating film 442 using the gate electrode layer 401 and the sidewall insulating layers 412a and 412b as masks.

In this embodiment, when the insulating film is etched, the insulating film over the gate electrode layer 401 is removed to expose the gate electrode layer 401, but the insulating film is left on the gate electrode layer 401. Sidewall insulating layers 412a and 412b may be formed. Further, a protective film may be formed over the gate electrode layer 401 in a later step. By protecting the gate electrode layer 401 in this manner, the gate electrode layer can be prevented from being reduced during etching. Note that the etching method may be a dry etching method or a wet etching method, and various etching methods can be used.

Next, a conductive film to be a source electrode layer and a drain electrode layer (including a wiring formed using the same layer) is formed over part of the sidewall insulating layers 412 a and 412 b and the amorphous oxide semiconductor film 443. To do. The conductive film is formed using a material that can withstand heat treatment performed later. As the conductive film used for the source electrode layer and the drain electrode layer, for example, a metal film containing an element selected from Al, Cr, Cu, Ta, Ti, Mo, and W, or metal nitriding containing the above-described element as a component A material film (titanium nitride film, molybdenum nitride film, tungsten nitride film) or the like can be used. Further, a refractory metal film such as Ti, Mo, W or the like or a metal nitride film thereof (titanium nitride film, molybdenum nitride film, tungsten nitride film) is provided on one or both of the lower side or the upper side of a metal film such as Al or Cu. It is good also as a structure which laminated | stacked. The conductive film used for the source electrode layer and the drain electrode layer may be formed using a conductive metal oxide. Examples of the conductive metal oxide include indium oxide (In ₂ O ₃ ), tin oxide (SnO ₂ ), zinc oxide (ZnO), indium tin oxide (In ₂ O ₃ —SnO ₂ ), and indium zinc oxide (In ₂ O ₃ —ZnO) or a metal oxide material containing silicon oxide can be used.

A resist mask is formed over the conductive film by a photolithography process, and selective etching is performed to form the source electrode layer 405a and the drain electrode layer 405b, and then the resist mask is removed (see FIG. 5D).

Next, an insulating film 407 is formed over the gate electrode layer 401, the sidewall insulating layers 412a and 412b, the source electrode layer 405a, and the drain electrode layer 405b (see FIG. 5E). The insulating film 407 may be a single layer or a stacked layer, but has a structure including an aluminum oxide film.

The thickness of the aluminum oxide film included in the insulating film 407 is 30 nm to 500 nm, preferably 50 nm to 200 nm. The insulating film 407 can be formed as appropriate by a method such as sputtering, in which an impurity such as water or hydrogen is not mixed into the insulating film 407. When hydrogen is contained in the insulating film 407, penetration of the hydrogen into the oxide semiconductor film or extraction of oxygen in the oxide semiconductor film due to hydrogen occurs, and the resistance of the oxide semiconductor film is reduced (N-type). As a result, a parasitic channel may be formed. Therefore, it is important not to use hydrogen in the deposition method so that the insulating film 407 contains as little hydrogen as possible.

The aluminum oxide film also preferably includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio in the crystalline state of the aluminum oxide. In this case, the oxygen content is set to exceed the stoichiometric composition ratio of aluminum oxide. Alternatively, the oxygen content is set to exceed the amount of oxygen in the case of a single crystal. Oxygen may be present between the aluminum oxide lattices. When the composition is expressed by AlO _x (x> 0), it is preferable to use an aluminum oxide film having an oxygen excess region where x exceeds 3/2. Such an oxygen-excess region may be present in a part (including the interface) of the aluminum oxide film.

In this embodiment, an aluminum oxide film with a thickness of 100 nm is formed as the insulating film 407 by a sputtering method. The aluminum oxide film can be formed by a sputtering method in a rare gas (typically argon) atmosphere, an oxygen atmosphere, or a mixed atmosphere of a rare gas and oxygen.

In the same manner as in the formation of the oxide semiconductor film, an adsorption vacuum pump (such as a cryopump) is preferably used in order to remove residual moisture in the deposition chamber of the insulating film 407. The concentration of impurities contained in the insulating film 407 formed in the deposition chamber evacuated using a cryopump can be reduced. Further, as an evacuation unit for removing moisture remaining in the deposition chamber of the insulating film 407, a turbo molecular pump provided with a cold trap may be used.

As a sputtering gas used for forming the insulating film 407, a high-purity gas from which impurities such as hydrogen, water, a hydroxyl group, or hydride are removed is preferably used.

In the case where the insulating film 407 is stacked, an inorganic insulating film such as a silicon oxide film, a silicon oxynitride film, an aluminum oxynitride film, or a gallium oxide film can be typically used in addition to the aluminum oxide film. FIG. 10B illustrates a transistor 440a as an example of the transistor 440 in which the insulating film 407 has a stacked structure of the insulating film 407a and the insulating film 407b.

As illustrated in FIG. 10B, the insulating film 407a is formed over the gate electrode layer 401, the sidewall insulating layers 412a and 412b, the source electrode layer 405a, and the drain electrode layer 405b, and the insulating film 407b is formed over the insulating film 407a. To do. For example, in this embodiment, as the insulating film 407a, a silicon oxide film in which a region where oxygen content is excessive with respect to the stoichiometric composition ratio in a crystalline state is used as silicon oxide is used, and the insulating film 407b is used. An aluminum oxide film is used.

Next, heat treatment is performed on the amorphous oxide semiconductor film 443 so that at least part of the amorphous oxide semiconductor film 443 is crystallized, so that a crystal including a crystal having a c-axis substantially perpendicular to the surface is obtained. An oxide semiconductor film 403 is formed.

The aluminum oxide film provided as the insulating film 407 over the amorphous oxide semiconductor film 443 has a high blocking effect (blocking effect) that prevents the film from passing through both impurities such as hydrogen and moisture and oxygen.

Therefore, the aluminum oxide film is formed into an oxide semiconductor film (amorphous oxide semiconductor film 443 and crystalline oxide semiconductor film 403) of impurities such as hydrogen and moisture which are factors of variation during and after the manufacturing process. It functions as a protective film for preventing entry and release of oxygen which is a main component material of the oxide semiconductor from the oxide semiconductor film (the amorphous oxide semiconductor film 443 and the crystalline oxide semiconductor film 403).

Since heat treatment for crystallizing the amorphous oxide semiconductor film 443 is performed in a state where the amorphous oxide semiconductor film 443 is covered with an aluminum oxide film provided as the insulating film 407, heating for crystallization is performed. By the treatment, release of oxygen from the amorphous oxide semiconductor film 443 can be prevented. Therefore, the obtained crystalline oxide semiconductor film 403 maintains the amount of oxygen contained in the amorphous oxide semiconductor film 443, and the oxide semiconductor has an oxygen content with respect to the stoichiometric composition ratio in the crystalline state. A film including an excessive region can be obtained.

Accordingly, the formed crystalline oxide semiconductor film 403 has high purity because entry of impurities such as hydrogen and moisture and release of excessively introduced oxygen are prevented by the aluminum oxide film. Includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio in the crystalline state.

In the crystalline oxide semiconductor film 403, oxygen vacancies exist at locations where oxygen is released. An oxide semiconductor that does not contain excess oxygen cannot be supplemented with other oxygen even if oxygen vacancies occur. However, the crystalline oxide semiconductor film 403 according to one embodiment of the disclosed invention is a film containing excess oxygen (in this embodiment, a CAAC-OS film containing excess oxygen), and the crystalline oxide semiconductor film Even if oxygen vacancies occur, 403 contains excess oxygen (preferably oxygen in excess of the stoichiometric composition ratio) in the film. Can be filled in the missing part.

Therefore, when the crystalline oxide semiconductor film 403 is used for the transistor 440, variation in threshold voltage Vth of the transistor due to oxygen deficiency and threshold voltage shift ΔVth can be reduced.

The temperature of heat treatment for crystallizing at least part of the amorphous oxide semiconductor film 443 is 300 ° C to 700 ° C, preferably 450 ° C to 650 ° C, more preferably 500 ° C, and still more preferably 550 ° C or more. And

For example, a substrate is introduced into an electric furnace which is one of heat treatment apparatuses, and the oxide semiconductor film is subjected to heat treatment at 450 ° C. for 1 hour in an oxygen atmosphere.

In the crystalline oxide semiconductor film 403 which is highly purified and in which oxygen vacancies are filled, impurities such as hydrogen and water are sufficiently removed, and the hydrogen concentration in the crystalline oxide semiconductor film 403 is 5 × 10 ^19. / Cm ³ or less, preferably 5 × 10 ¹⁸ / cm ³ or less.

Such a crystalline oxide semiconductor film 403 has very few carriers (close to zero), and the carrier concentration is less than 1 × 10 ¹⁴ / cm ³ , preferably less than 1 × 10 ¹² / cm ³ , and more preferably 1 It is less than × 10 ¹¹ / cm ³ .

Through the above steps, the transistor 440 is formed (see FIG. 5F). The transistor 440 is a transistor including a crystalline oxide semiconductor film that is highly purified and contains excess oxygen that fills oxygen vacancies. Thus, the transistor 440 is electrically stable because variation in electrical characteristics is suppressed.

A transistor 440 using the crystalline oxide semiconductor film 403 which is manufactured using this embodiment and is highly purified and contains oxygen excessively to fill oxygen vacancies has an off-state current value (off-state current value) as follows: 100 zA / μm (1 zA (zeptoampere) is 1 × 10 ⁻²¹ A) or less, preferably 10 zA / μm or less, more preferably 1 zA / μm or less, more preferably 100 yA / μm or less at room temperature per channel width of 1 μm. Can be lowered.

As described above, a semiconductor device including an oxide semiconductor having stable electrical characteristics can be provided. Therefore, a highly reliable semiconductor device can be provided.

(Embodiment 6)
In this embodiment, another embodiment of a semiconductor device and a method for manufacturing the semiconductor device will be described with reference to FIGS. The same portions as those in the above embodiment or portions and processes having similar functions can be performed in the same manner as in the above embodiment, and repeated description is omitted. Detailed descriptions of the same parts are omitted.

In this embodiment, an example in which the oxygen introduction step into the amorphous oxide semiconductor film is performed through the gate insulating film after the gate electrode layer is formed in the method for manufacturing a semiconductor device according to the disclosed invention.

6A to 6E illustrate an example of a method for manufacturing the transistor 440 in this embodiment.

First, the insulating film 436 is formed over the substrate 400. Then, an amorphous oxide semiconductor film 492 is formed over the insulating film 436. A gate insulating film 442 is formed so as to cover the amorphous oxide semiconductor film 492.

Then, the gate electrode layer 401 is formed over the gate insulating film 442 (see FIG. 6A).

Further, heat treatment for removing (dehydrating or dehydrogenating) excess hydrogen (including water and a hydroxyl group) may be performed on the amorphous oxide semiconductor film 492.

Next, oxygen 431 (including at least one of oxygen radicals, oxygen atoms, and oxygen ions) is introduced into the amorphous oxide semiconductor film 492 so that oxygen is supplied to the amorphous oxide semiconductor film 492. Do.

In this embodiment, after the gate electrode layer 401 is formed, oxygen 431 is implanted into the amorphous oxide semiconductor film 492 through the gate insulating film 442 by an ion implantation method. Through the implantation process of oxygen 431, the amorphous oxide semiconductor film 492 is formed into an amorphous oxide film in which an oxide semiconductor includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio in a crystalline state. The semiconductor film 443 is formed (see FIG. 6B).

When oxygen is introduced, the gate electrode layer 401 serves as a mask, and oxygen 431 may not be directly introduced into the region of the amorphous oxide semiconductor film 492 on which the gate electrode layer 401 overlaps, but the width of the gate electrode layer 401 is The gate electrode layer 401 overlaps oxygen introduced into the amorphous oxide semiconductor film 443 by heat treatment for crystallization of the amorphous oxide semiconductor film 443 because it is narrow (eg, at a submicron level). It can also be diffused into the region of the amorphous oxide semiconductor film 443.

Oxygen vacancies existing in the amorphous oxide semiconductor film 443 can be filled with the supplied oxygen 431.

Sidewall insulating layers 412 a and 412 b having a sidewall structure and a gate insulating film 402 are formed on side surfaces of the gate electrode layer 401.

The gate insulating film 402 can be formed by etching the gate insulating film 442 using the gate electrode layer 401 and the sidewall insulating layers 412a and 412b as masks.

Next, a conductive film to be a source electrode layer and a drain electrode layer (including a wiring formed using the same layer) is formed over part of the sidewall insulating layers 412 a and 412 b and the amorphous oxide semiconductor film 443. To do.

A resist mask is formed over the conductive film by a photolithography process and selective etching is performed to form the source electrode layer 405a and the drain electrode layer 405b, and then the resist mask is removed (see FIG. 6C).

Next, an insulating film 407 is formed over the gate electrode layer 401, the sidewall insulating layers 412a and 412b, the source electrode layer 405a, and the drain electrode layer 405b (see FIG. 6D). The insulating film 407 may be a single layer or a stacked layer, but has a structure including an aluminum oxide film.

In this embodiment, an aluminum oxide film with a thickness of 100 nm is formed as the insulating film 407 by a sputtering method.

Next, the amorphous oxide semiconductor film 443 is subjected to heat treatment, and at least part of the amorphous oxide semiconductor film 443 is crystallized, so that the crystalline oxide semiconductor film 403 is formed. Further, by this heat treatment, oxygen diffuses throughout the amorphous oxide semiconductor film 443, and oxygen is supplied throughout the film.

In this embodiment, as the crystalline oxide semiconductor film 403, a crystalline oxide semiconductor film 403 including a crystal having a c-axis substantially perpendicular to the surface is formed.

The aluminum oxide film provided as the insulating film 407 over the amorphous oxide semiconductor film 443 has a high blocking effect (blocking effect) that prevents the film from passing through both impurities such as hydrogen and moisture and oxygen.

Therefore, the aluminum oxide film is formed into an oxide semiconductor film (amorphous oxide semiconductor film 443 and crystalline oxide semiconductor film 403) of impurities such as hydrogen and moisture which are factors of variation during and after the manufacturing process. It functions as a protective film for preventing entry and release of oxygen which is a main component material of the oxide semiconductor from the oxide semiconductor film (the amorphous oxide semiconductor film 443 and the crystalline oxide semiconductor film 403).

Since heat treatment for crystallizing the amorphous oxide semiconductor film 443 is performed in a state where the amorphous oxide semiconductor film 443 is covered with an aluminum oxide film provided as the insulating film 407, heating for crystallization is performed. By the treatment, release of oxygen from the amorphous oxide semiconductor film 443 can be prevented. Therefore, the obtained crystalline oxide semiconductor film 403 maintains the amount of oxygen contained in the amorphous oxide semiconductor film 443, and the oxide semiconductor has an oxygen content with respect to the stoichiometric composition ratio in the crystalline state. A film including an excessive region can be obtained.

Accordingly, the formed crystalline oxide semiconductor film 403 has high purity because entry of impurities such as hydrogen and moisture and release of excessively introduced oxygen are prevented by the aluminum oxide film. Includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio in the crystalline state.

In the crystalline oxide semiconductor film 403, oxygen vacancies exist at locations where oxygen is released. An oxide semiconductor that does not contain excess oxygen cannot be supplemented with other oxygen even if oxygen vacancies occur. However, the crystalline oxide semiconductor film 403 according to one embodiment of the disclosed invention is a film containing excess oxygen (in this embodiment, a CAAC-OS film containing excess oxygen), and the crystalline oxide semiconductor film Even if oxygen vacancies occur, 403 contains excess oxygen (preferably oxygen in excess of the stoichiometric composition ratio) in the film. Can be filled in the missing part.

Therefore, when the crystalline oxide semiconductor film 403 is used for the transistor 440, variation in threshold voltage Vth of the transistor due to oxygen deficiency and threshold voltage shift ΔVth can be reduced.

Through the above process, the transistor 440 is formed (see FIG. 6E). The transistor 440 is a transistor including a crystalline oxide semiconductor film that is highly purified and contains excess oxygen that fills oxygen vacancies. Thus, the transistor 440 is electrically stable because variation in electrical characteristics is suppressed.

A transistor 440 using the crystalline oxide semiconductor film 403 which is manufactured using this embodiment and is highly purified and contains oxygen excessively to fill oxygen vacancies has an off-state current value (off-state current value) as follows: 100 zA / μm (1 zA (zeptoampere) is 1 × 10 ⁻²¹ A) or less, preferably 10 zA / μm or less, more preferably 1 zA / μm or less, more preferably 100 yA / μm or less at room temperature per channel width of 1 μm. Can be lowered.

As described above, a semiconductor device including an oxide semiconductor having stable electrical characteristics can be provided. Therefore, a highly reliable semiconductor device can be provided.

(Embodiment 7)
In this embodiment, another embodiment of a semiconductor device and a method for manufacturing the semiconductor device will be described with reference to FIGS. The same portions as those in the above embodiment or portions and processes having similar functions can be performed in the same manner as in the above embodiment, and repeated description is omitted. Detailed descriptions of the same parts are omitted.

In this embodiment, an example in which the step of introducing oxygen into an amorphous oxide semiconductor film is performed through an insulating film provided over a transistor in the method for manufacturing a semiconductor device according to the disclosed invention will be described.

7A to 7E illustrate an example of a method for manufacturing the transistor 420 in this embodiment.

First, the insulating film 436 is formed over the substrate 400. Then, an amorphous oxide semiconductor film 492 is formed over the insulating film 436. A gate insulating film 442 is formed so as to cover the amorphous oxide semiconductor film 492.

Then, the gate electrode layer 401 is formed over the gate insulating film 442 (see FIG. 7A).

Note that in this embodiment, an example is described in which a sidewall insulating layer 442 provided as a continuous film is formed without forming a sidewall insulating layer having a sidewall structure and processing a gate insulating film into an island shape.

Further, heat treatment for removing (dehydrating or dehydrogenating) excess hydrogen (including water and a hydroxyl group) may be performed on the amorphous oxide semiconductor film 492.

Next, an insulating film 407 is formed over the gate insulating film 442 and the gate electrode layer 401 (see FIG. 7B). The insulating film 407 may be a single layer or a stacked layer, but has a structure including an aluminum oxide film.

In this embodiment, an aluminum oxide film with a thickness of 100 nm is formed as the insulating film 407 by a sputtering method.

Next, oxygen 431 (including at least one of oxygen radicals, oxygen atoms, and oxygen ions) is introduced into the amorphous oxide semiconductor film 492 so that oxygen is supplied to the amorphous oxide semiconductor film 492. Do.

In this embodiment, after the insulating film 407 is formed, oxygen 431 is implanted into the amorphous oxide semiconductor film 492 through the gate insulating film 442 and the insulating film 407 by an ion implantation method. Through the implantation process of oxygen 431, the amorphous oxide semiconductor film 492 is formed into an amorphous oxide film in which an oxide semiconductor includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio in a crystalline state. The semiconductor film 443 is formed (see FIG. 7C).

When oxygen is introduced, the gate electrode layer 401 serves as a mask, and oxygen 431 may not be directly introduced into the region of the amorphous oxide semiconductor film 492 on which the gate electrode layer 401 overlaps, but the width of the gate electrode layer 401 is Since it is narrow (eg, 0.35 μm), the gate electrode layer 401 overlaps oxygen introduced into the amorphous oxide semiconductor film 443 by heat treatment for crystallization of the amorphous oxide semiconductor film 443. It can also be diffused into the region of the amorphous oxide semiconductor film 443.

Oxygen vacancies existing in the amorphous oxide semiconductor film 443 can be filled with the supplied oxygen 431.

Next, heat treatment is performed on the amorphous oxide semiconductor film 443 to crystallize at least part of the amorphous oxide semiconductor film 443, so that a crystalline oxide semiconductor film 403 is formed (FIG. 7D). reference). Further, by this heat treatment, oxygen diffuses throughout the amorphous oxide semiconductor film 443, and oxygen is supplied throughout the film.

In this embodiment, as the crystalline oxide semiconductor film 403, a crystalline oxide semiconductor film 403 including a crystal having a c-axis substantially perpendicular to the surface is formed.

The aluminum oxide film provided as the insulating film 407 over the amorphous oxide semiconductor film 443 has a high blocking effect (blocking effect) that prevents the film from passing through both impurities such as hydrogen and moisture and oxygen.

Therefore, the aluminum oxide film is formed into an oxide semiconductor film (amorphous oxide semiconductor film 443 and crystalline oxide semiconductor film 403) of impurities such as hydrogen and moisture which are factors of variation during and after the manufacturing process. It functions as a protective film for preventing entry and release of oxygen which is a main component material of the oxide semiconductor from the oxide semiconductor film (the amorphous oxide semiconductor film 443 and the crystalline oxide semiconductor film 403).

Since heat treatment for crystallizing the amorphous oxide semiconductor film 443 is performed in a state where the amorphous oxide semiconductor film 443 is covered with an aluminum oxide film provided as the insulating film 407, heating for crystallization is performed. By the treatment, release of oxygen from the amorphous oxide semiconductor film 443 can be prevented. Therefore, the obtained crystalline oxide semiconductor film 403 maintains the amount of oxygen contained in the amorphous oxide semiconductor film 443, and the oxide semiconductor has an oxygen content with respect to the stoichiometric composition ratio in the crystalline state. A film including an excessive region can be obtained.

Accordingly, the formed crystalline oxide semiconductor film 403 has high purity because entry of impurities such as hydrogen and moisture and release of excessively introduced oxygen are prevented by the aluminum oxide film. Includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio in the crystalline state.

In the crystalline oxide semiconductor film 403, oxygen vacancies exist at locations where oxygen is released. An oxide semiconductor that does not contain excess oxygen cannot be supplemented with other oxygen even if oxygen vacancies occur. However, the crystalline oxide semiconductor film 403 according to one embodiment of the disclosed invention is a film containing excess oxygen (in this embodiment, a CAAC-OS film containing excess oxygen), and the crystalline oxide semiconductor film Even if oxygen vacancies occur, 403 contains excess oxygen (preferably oxygen in excess of the stoichiometric composition ratio) in the film. Can be filled in the missing part.

Therefore, when the crystalline oxide semiconductor film 403 is used for the transistor 420, variation in threshold voltage Vth of the transistor and shift ΔVth in threshold voltage due to oxygen deficiency can be reduced.

Further, a planarization insulating film may be formed in order to reduce surface unevenness due to the transistor. As the planarization insulating film, an organic material such as polyimide, acrylic, or benzocyclobutene resin can be used. In addition to the organic material, a low dielectric constant material (low-k material) or the like can be used. Note that the planarization insulating film may be formed by stacking a plurality of insulating films formed using these materials.

In this embodiment, a planarization insulating film 415 is formed over the insulating film 407. In addition, an opening reaching the crystalline oxide semiconductor film 403 is formed in the gate insulating film 442, the insulating film 407, and the planarization insulating film 415, and the source electrode layer electrically connected to the crystalline oxide semiconductor film 403 is formed in the opening. 405a and a drain electrode layer 405b are formed.

Through the above process, the transistor 420 is formed (see FIG. 7E). The transistor 420 is a transistor including a crystalline oxide semiconductor film which is highly purified and contains excess oxygen which fills oxygen vacancies. Thus, the transistor 420 has stable electrical characteristics and is electrically stable.

In the case where the insulating film 407 is stacked, an inorganic insulating film such as a silicon oxide film, a silicon oxynitride film, an aluminum oxynitride film, or a gallium oxide film can be typically used in addition to the aluminum oxide film. FIG. 10C illustrates a transistor 420a as an example in which the insulating film 407 has a stacked structure of the insulating film 407a and the insulating film 407b in the transistor 420.

As shown in FIG. 10C, an insulating film 407a is formed over the gate insulating film 402 and the gate electrode layer 401, and an insulating film 407b is formed over the insulating film 407a. For example, in this embodiment, as the insulating film 407a, a silicon oxide film including a region in which oxygen content is excessive with respect to the stoichiometric composition ratio of silicon oxide in a crystalline state is used, and the insulating film 407b is used. An aluminum oxide film is used.

In the case where the insulating film 407 has a stacked structure of the insulating films 407a and 407b, the oxygen introduction step into the amorphous oxide semiconductor film 492 can be performed through the stacked insulating films 407a and 407b.

A transistor 420 using the crystalline oxide semiconductor film 403 which is manufactured using this embodiment and is highly purified and contains excess oxygen which fills oxygen vacancies has an off-state current value (off-state current value) as follows: 100 zA / μm (1 zA (zeptoampere) is 1 × 10 ⁻²¹ A) or less, preferably 10 zA / μm or less, more preferably 1 zA / μm or less, more preferably 100 yA / μm or less at room temperature per channel width of 1 μm. Can be lowered.

As described above, a semiconductor device including an oxide semiconductor having stable electrical characteristics can be provided. Therefore, a highly reliable semiconductor device can be provided.

(Embodiment 8)
In this embodiment, another embodiment of a semiconductor device and a method for manufacturing the semiconductor device will be described with reference to FIGS. The same portions as those in the above embodiment or portions and processes having similar functions can be performed in the same manner as in the above embodiment, and repeated description is omitted. Detailed descriptions of the same parts are omitted.

In this embodiment, an example of a method for manufacturing a transistor in which the connection structure between the source and drain electrode layers and the crystalline oxide semiconductor film is different from that in Embodiment 5 will be described.

8A to 8F illustrate an example of a method for manufacturing the transistor 450 in this embodiment.

First, the insulating film 436 is formed over the substrate 400.

Next, a conductive film to be a source electrode layer and a drain electrode layer (including a wiring formed using the same layer) is formed over the insulating film 436.

A resist mask is formed over the conductive film by a photolithography step, and selective etching is performed to form the source electrode layer 405a and the drain electrode layer 405b, and then the resist mask is removed (see FIG. 8A).

Then, an amorphous oxide semiconductor film 492 is formed over the insulating film 436, the source electrode layer 405a, and the drain electrode layer 405b (see FIG. 8B). A gate insulating film 402 is formed so as to cover the amorphous oxide semiconductor film 492 (see FIG. 8C).

Further, heat treatment for removing (dehydrating or dehydrogenating) excess hydrogen (including water and a hydroxyl group) may be performed on the amorphous oxide semiconductor film 492.

Next, oxygen 431 (including at least one of oxygen radicals, oxygen atoms, and oxygen ions) is introduced into the amorphous oxide semiconductor film 492 so that oxygen is supplied to the amorphous oxide semiconductor film 492. Do.

In this embodiment, oxygen 431 is implanted into the amorphous oxide semiconductor film 492 through the gate insulating film 402 by an ion implantation method. Through the implantation process of oxygen 431, the amorphous oxide semiconductor film 492 is formed into an amorphous oxide film in which an oxide semiconductor includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio in a crystalline state. The semiconductor film 443 is formed (see FIG. 8D).

Oxygen vacancies existing in the amorphous oxide semiconductor film 443 can be filled with the supplied oxygen 431.

Then, the gate electrode layer 401 is formed over the gate insulating film 402.

In this embodiment, an example in which a sidewall insulating layer having a sidewall structure is not provided on a side surface of the gate electrode layer 401 is described. However, as described in Embodiment 5, a sidewall insulating layer having a sidewall structure is provided and the gate insulating film 402 is formed. May be processed into islands.

Next, an insulating film 407 is formed over the gate insulating film 402 and the gate electrode layer 401 (see FIG. 8E). The insulating film 407 may be a single layer or a stacked layer, but has a structure including an aluminum oxide film.

In this embodiment, an aluminum oxide film with a thickness of 100 nm is formed as the insulating film 407 by a sputtering method.

Next, the amorphous oxide semiconductor film 443 is subjected to heat treatment, and at least part of the amorphous oxide semiconductor film 443 is crystallized, so that the crystalline oxide semiconductor film 403 is formed.

In this embodiment, as the crystalline oxide semiconductor film 403, a crystalline oxide semiconductor film 403 including a crystal having a c-axis substantially perpendicular to the surface is formed.

The aluminum oxide film provided as the insulating film 407 over the amorphous oxide semiconductor film 443 has a high blocking effect (blocking effect) that prevents the film from passing through both impurities such as hydrogen and moisture and oxygen.

Therefore, the aluminum oxide film is formed into an oxide semiconductor film (amorphous oxide semiconductor film 443 and crystalline oxide semiconductor film 403) of impurities such as hydrogen and moisture which are factors of variation during and after the manufacturing process. It functions as a protective film for preventing entry and release of oxygen which is a main component material of the oxide semiconductor from the oxide semiconductor film (the amorphous oxide semiconductor film 443 and the crystalline oxide semiconductor film 403).

Since heat treatment for crystallizing the amorphous oxide semiconductor film 443 is performed in a state where the amorphous oxide semiconductor film 443 is covered with an aluminum oxide film provided as the insulating film 407, heating for crystallization is performed. By the treatment, release of oxygen from the amorphous oxide semiconductor film 443 can be prevented. Therefore, the obtained crystalline oxide semiconductor film 403 maintains the amount of oxygen contained in the amorphous oxide semiconductor film 443, and the oxide semiconductor has an oxygen content with respect to the stoichiometric composition ratio in the crystalline state. A film including an excessive region can be obtained.

Accordingly, the formed crystalline oxide semiconductor film 403 has high purity because entry of impurities such as hydrogen and moisture and release of excessively introduced oxygen are prevented by the aluminum oxide film. Includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio in the crystalline state.

In the crystalline oxide semiconductor film 403, oxygen vacancies exist at locations where oxygen is released. An oxide semiconductor that does not contain excess oxygen cannot be supplemented with other oxygen even if oxygen vacancies occur. However, the crystalline oxide semiconductor film 403 according to one embodiment of the disclosed invention is a film containing excess oxygen (in this embodiment, a CAAC-OS film containing excess oxygen), and the crystalline oxide semiconductor film Even if oxygen vacancies occur, 403 contains excess oxygen (preferably oxygen in excess of the stoichiometric composition ratio) in the film. Can be filled in the missing part.

Therefore, when the crystalline oxide semiconductor film 403 is used for the transistor 450, variation in threshold voltage Vth of the transistor due to oxygen deficiency and threshold voltage shift ΔVth can be reduced.

In the case where the insulating film 407 is stacked, an inorganic insulating film such as a silicon oxide film, a silicon oxynitride film, an aluminum oxynitride film, or a gallium oxide film can be typically used in addition to the aluminum oxide film. FIG. 10D illustrates a transistor 450a as an example in which the insulating film 407 has a stacked structure of the insulating film 407a and the insulating film 407b in the transistor 450.

As shown in FIG. 10D, an insulating film 407a is formed over the gate insulating film 402 and the gate electrode layer 401, and an insulating film 407b is formed over the insulating film 407a. For example, in this embodiment, as the insulating film 407a, a silicon oxide film including a region in which oxygen content is excessive with respect to the stoichiometric composition ratio of silicon oxide in a crystalline state is used, and the insulating film 407b is used. An aluminum oxide film is used.

Through the above steps, the transistor 450 is formed (see FIG. 8F). The transistor 450 is a transistor having a crystalline oxide semiconductor film that is highly purified and contains excess oxygen that fills oxygen vacancies. Thus, the transistor 450 is electrically stable because variation in electrical characteristics is suppressed.

A transistor 450 using a crystalline oxide semiconductor film 403 which is manufactured using this embodiment and which includes oxygen that is highly purified and fills oxygen vacancies excessively has an off-state current value (off-state current value) as follows: 100 zA / μm (1 zA (zeptoampere) is 1 × 10 ⁻²¹ A) or less, preferably 10 zA / μm or less, more preferably 1 zA / μm or less, more preferably 100 yA / μm or less at room temperature per channel width of 1 μm. Can be lowered.

As described above, a semiconductor device including an oxide semiconductor having stable electrical characteristics can be provided. Therefore, a highly reliable semiconductor device can be provided.

(Embodiment 9)
In this embodiment, another embodiment of a method for manufacturing a semiconductor device will be described. The same portions as those in the above embodiment or portions and processes having similar functions can be performed in the same manner as in the above embodiment, and repeated description is omitted. Detailed descriptions of the same parts are omitted.

Note that in this embodiment, an example of an oxygen introduction step that can be used in the manufacturing process of the transistor 450 described in Embodiment 8 is described using the transistor 450c.

FIG. 9A illustrates an example in which oxygen 431 is directly introduced into the amorphous oxide semiconductor film 492 after the step of FIG. By the introduction process of oxygen 431, the amorphous oxide semiconductor film 492 is formed into an amorphous oxide film in which an oxide semiconductor includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio in a crystalline state. The physical semiconductor film 443 is formed. Oxygen vacancies existing in the amorphous oxide semiconductor film 443 can be filled with the supplied oxygen 431. Note that in the case where oxygen is directly introduced into the exposed amorphous oxide semiconductor film 492 as in FIG. 9A, plasma treatment can be used.

In the transistor that can be manufactured according to one embodiment of the present invention, the positional relationship between the gate electrode layer 401 and the source electrode layer 405a and the drain electrode layer 405b is formed without overlapping with the gate insulating film 402 interposed therebetween. Alternatively, it may be partially overlapped.

For example, in the transistor 450 illustrated in FIG. 8 in Embodiment 8, the source electrode layer 405a, the drain electrode layer 405b, and the gate electrode layer 401 are interposed between the gate insulating film 402 and the crystalline oxide semiconductor film 403. It is an example of the structure which overlaps partially via.

In this embodiment, the transistor 450c illustrated in FIGS. 9B and 9C includes a source electrode layer 405a, a drain electrode layer 405b, a gate electrode layer 401, a gate insulating film 402, and a crystalline oxide semiconductor film 403. This is an example of a structure that does not overlap with each other.

FIG. 9B illustrates an example in which after the gate electrode layer 401 is formed over the gate insulating film 402, oxygen 431 is introduced into the amorphous oxide semiconductor film 492 through the gate insulating film 402. By the introduction process of oxygen 431, the amorphous oxide semiconductor film 492 is formed into an amorphous oxide film in which an oxide semiconductor includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio in a crystalline state. The physical semiconductor film 443 is formed. Oxygen vacancies existing in the amorphous oxide semiconductor film 443 can be filled with the supplied oxygen 431.

In FIG. 9C, after an insulating film 407 is formed over the gate insulating film 402 and the gate electrode layer 401, oxygen 431 is introduced into the amorphous oxide semiconductor film 492 through the gate insulating film 402 and the insulating film 407. This is an example. By the introduction process of oxygen 431, the amorphous oxide semiconductor film 492 is formed into an amorphous oxide film in which an oxide semiconductor includes a region where the oxygen content is excessive with respect to the stoichiometric composition ratio in a crystalline state. The physical semiconductor film 443 is formed. Oxygen vacancies existing in the amorphous oxide semiconductor film 443 can be filled with the supplied oxygen 431.

9B and 9C, when the step of introducing oxygen 431 into the amorphous oxide semiconductor film 492 is performed after the gate insulating film 402 and the gate electrode layer 401 are formed, the gate electrode layer 401 and the source When the electrode layer 405a and the drain electrode layer 405b do not overlap with each other, the oxygen 431 to the amorphous oxide semiconductor film 492 located between the gate electrode layer 401 and the source electrode layer 405a and drain electrode layer 405b is used. Can be relatively easily introduced.

As described above, the step of introducing oxygen into the crystalline oxide semiconductor film may be performed after dehydration or dehydrogenation treatment, and is not particularly limited. Further, oxygen may be introduced into the oxide semiconductor film subjected to the dehydration or dehydrogenation treatment a plurality of times.

The transistor manufactured through the above steps is a transistor having a crystalline oxide semiconductor film that is highly purified and contains oxygen in excess to fill oxygen vacancies. Therefore, the transistor has stable electrical characteristics with less variation in electrical characteristics.

A semiconductor device including an oxide semiconductor having stable electrical characteristics can be provided. Therefore, a highly reliable semiconductor device can be provided.

This embodiment can be implemented in appropriate combination with any of the other embodiments.

(Embodiment 10)
In this embodiment, another embodiment of a semiconductor device and a method for manufacturing the semiconductor device will be described with reference to FIGS. The same portions as those in the above embodiment or portions and processes having similar functions can be performed in the same manner as in the above embodiment, and repeated description is omitted. Detailed descriptions of the same parts are omitted.

This embodiment is an example in which an impurity region functioning as a source region and a drain region is formed in a crystalline oxide semiconductor film in the method for manufacturing a semiconductor device according to the disclosed invention. The impurity regions functioning as a source region and a drain region can be formed by introducing an impurity (also referred to as a dopant) that changes conductivity into the crystalline oxide semiconductor film.

The concentration of the dopant in the impurity regions functioning as the source region and the drain region is preferably 5 × 10 ¹⁸ / cm ³ or more and 1 × 10 ²² / cm ³ or less.

The dopant to be introduced is a group 15 element and boron, specifically, one or more selected from phosphorus, arsenic, antimony, and boron. As a method for introducing a dopant into the crystalline oxide semiconductor film, an ion doping method or an ion implantation method can be used.

When the dopant is introduced by the ion doping method or the ion implantation method, the substrate may be heated.

Note that the treatment for introducing the dopant into the crystalline oxide semiconductor film may be performed a plurality of times, and a plurality of types of dopant may be used.

The impurity region into which the dopant is introduced may be partially made amorphous by the introduction of the dopant. In this case, crystallinity can be recovered by performing heat treatment after the introduction of the dopant.

FIG. 11A illustrates an example of the transistor 440b in which impurity regions 404a and 404b functioning as a source region and a drain region are provided in the crystalline oxide semiconductor film 403 in the transistor 440 described in Embodiment 5 or 6 Indicates. The impurity regions 404a and 404b are formed by introducing a dopant into the crystalline oxide semiconductor film 403 before forming the source electrode layer 405a and the drain electrode layer 405b using the gate electrode layer 401 and the sidewall insulating layers 412a and 412b as masks. be able to.

FIG. 11B illustrates an example of the transistor 420b in which impurity regions 404a and 404b functioning as a source region and a drain region are provided in the crystalline oxide semiconductor film 403 in the transistor 420 described in Embodiment 7. The impurity regions 404a and 404b can be formed by introducing a dopant into the crystalline oxide semiconductor film 403 using the gate electrode layer 401 as a mask.

FIG. 11C illustrates an example of the transistor 450b in which impurity regions 404a and 404b functioning as a source region and a drain region are provided in the crystalline oxide semiconductor film 403 in the transistor 450 described in Embodiment 8. The impurity regions 404a and 404b can be formed by introducing a dopant into the crystalline oxide semiconductor film 403 using the gate electrode layer 401 as a mask.

By providing an impurity region functioning as a source region or a drain region, an electric field applied to a channel formation region formed between the impurity regions can be reduced. In addition, by electrically connecting the crystalline oxide semiconductor film and the electrode layer in the impurity region, contact resistance between the crystalline oxide semiconductor film and the electrode layer can be reduced. Accordingly, the electrical characteristics of the transistor can be improved.

This embodiment can be implemented in appropriate combination with any of the other embodiments.

(Embodiment 11)
A semiconductor device having a display function (also referred to as a display device) can be manufactured using the transistor described as an example in any of Embodiments 1 to 10. In addition, part or the whole of a driver circuit including a transistor can be formed over the same substrate as the pixel portion to form a system-on-panel.

In FIG. 13A, a sealant 4005 is provided so as to surround the pixel portion 4002 provided over the first substrate 4001 and sealed with the second substrate 4006. In FIG. 13A, a single crystal semiconductor film or a polycrystalline semiconductor film is formed over a separately prepared substrate in a region different from the region surrounded by the sealant 4005 over the first substrate 4001. A scan line driver circuit 4004 and a signal line driver circuit 4003 are mounted. In addition, a variety of signals and potentials are supplied to a separately formed signal line driver circuit 4003, the scan line driver circuit 4004, and the pixel portion 4002 from FPCs (Flexible Printed Circuits) 4018a and 4018b.

13B and 13C, a sealant 4005 is provided so as to surround the pixel portion 4002 provided over the first substrate 4001 and the scan line driver circuit 4004. A second substrate 4006 is provided over the pixel portion 4002 and the scan line driver circuit 4004. Therefore, the pixel portion 4002 and the scan line driver circuit 4004 are sealed together with the display element by the first substrate 4001, the sealant 4005, and the second substrate 4006. 13B and 13C, a single crystal semiconductor film or a polycrystalline semiconductor film is formed over a separately prepared substrate in a region different from the region surrounded by the sealant 4005 over the first substrate 4001. The formed signal line driver circuit 4003 is mounted. 13B and 13C, a signal line driver circuit 4003 which is formed separately, and various signals and potentials which are supplied to the scan line driver circuit 4004 or the pixel portion 4002 are supplied from an FPC 4018.

13B and 13C illustrate an example in which the signal line driver circuit 4003 is separately formed and mounted on the first substrate 4001, the invention is not limited to this structure. The scan line driver circuit may be separately formed and then mounted, or only part of the signal line driver circuit or part of the scan line driver circuit may be separately formed and then mounted.

Note that a connection method of a driver circuit which is separately formed is not particularly limited, and a COG (Chip On Glass) method, a wire bonding method, a TAB (Tape Automated Bonding) method, or the like can be used. FIG. 13A illustrates an example in which the signal line driver circuit 4003 and the scan line driver circuit 4004 are mounted by a COG method, and FIG. 13B illustrates an example in which the signal line driver circuit 4003 is mounted by a COG method. FIG. 13C illustrates an example in which the signal line driver circuit 4003 is mounted by a TAB method.

The display device includes a panel in which the display element is sealed, and a module in which an IC including a controller is mounted on the panel.

Note that a display device in this specification means an image display device, a display device, or a light source (including a lighting device). Further, an IC (integrated circuit) is directly mounted on a connector, for example, a module with an FPC or TAB tape or TCP attached, a module with a printed wiring board provided on the end of the TAB tape or TCP, or a display element by the COG method. All modules are included in the display device.

In addition, the pixel portion and the scan line driver circuit provided over the first substrate include a plurality of transistors, and the transistor shown as an example in any of Embodiments 1 to 10 can be used.

As a display element provided in the display device, a liquid crystal element (also referred to as a liquid crystal display element) or a light-emitting element (also referred to as a light-emitting display element) can be used. The light-emitting element includes, in its category, an element whose luminance is controlled by current or voltage, and specifically includes inorganic EL (Electro Luminescence), organic EL, and the like. In addition, a display medium whose contrast is changed by an electric effect, such as electronic ink, can be used.

One embodiment of a semiconductor device is described with reference to FIGS. FIG. 14 corresponds to a cross-sectional view taken along line MN in FIG.

As shown in FIGS. 13 and 14, the semiconductor device includes a connection terminal electrode 4015 and a terminal electrode 4016. The connection terminal electrode 4015 and the terminal electrode 4016 are connected to a terminal of the FPC 4018 and an anisotropic conductive film 4019. Are electrically connected.

The connection terminal electrode 4015 is formed using the same conductive film as the first electrode layer 4030, and the terminal electrode 4016 is formed using the same conductive film as the source and drain electrode layers of the transistors 4010 and 4011.

In addition, the pixel portion 4002 and the scan line driver circuit 4004 provided over the first substrate 4001 include a plurality of transistors. In FIG. 14, the transistor 4010 included in the pixel portion 4002 and the scan line driver circuit 4004 are included. The transistor 4011 included in FIG. In FIG. 14A, an insulating film 4020 and an insulating film 4032 are provided over the transistors 4010 and 4011. In FIG. 14B, an insulating film 4021 is further provided. Note that the insulating film 4023 is an insulating film functioning as a base film.

As the transistor 4010 and the transistor 4011, the transistor described in any of Embodiments 1 to 10 can be used. In this embodiment, an example in which a transistor having a structure similar to that of the transistor 410 described in Embodiment 1 is used is described.

The transistors 4010 and 4011 are transistors each having a crystalline oxide semiconductor film which is highly purified and contains excess oxygen which fills oxygen vacancies. Thus, the transistor 4010 and the transistor 4011 are electrically stable because variations in electrical characteristics are suppressed.

Therefore, a highly reliable semiconductor device can be provided as the semiconductor device of this embodiment illustrated in FIGS.

In this embodiment, the conductive layer is provided over the insulating film so as to overlap with the channel formation region of the crystalline oxide semiconductor film of the transistor 4011 for the driver circuit. By providing the conductive layer so as to overlap with the channel formation region of the crystalline oxide semiconductor film, the amount of change in the threshold voltage of the transistor 4011 before and after the bias-thermal stress test (BT test) can be further reduced. In addition, the potential of the conductive layer may be the same as or different from that of the gate electrode layer of the transistor 4011, and the conductive layer can function as a second gate electrode layer. Further, the potential of the conductive layer may be GND, 0 V, or a floating state.

The conductive layer also has a function of shielding an external electric field, that is, preventing the external electric field from acting on the inside (a circuit portion including a transistor) (particularly, an electrostatic shielding function against static electricity). With the shielding function of the conductive layer, the electrical characteristics of the transistor can be prevented from changing due to the influence of an external electric field such as static electricity.

A transistor 4010 provided in the pixel portion 4002 is electrically connected to a display element to form a display panel. The display element is not particularly limited as long as display can be performed, and various display elements can be used.

FIG. 14A illustrates an example of a liquid crystal display device using a liquid crystal element as a display element. In FIG. 14A, a liquid crystal element 4013 which is a display element includes a first electrode layer 4030, a second electrode layer 4031, and a liquid crystal layer 4008. Note that insulating films 4032 and 4033 functioning as alignment films are provided so as to sandwich the liquid crystal layer 4008. The second electrode layer 4031 is provided on the second substrate 4006 side, and the first electrode layer 4030 and the second electrode layer 4031 are stacked with the liquid crystal layer 4008 interposed therebetween.

Reference numeral 4035 denotes a columnar spacer obtained by selectively etching the insulating film, and is provided for controlling the film thickness (cell gap) of the liquid crystal layer 4008. A spherical spacer may be used.

When a liquid crystal element is used as the display element, a thermotropic liquid crystal, a low molecular liquid crystal, a polymer liquid crystal, a polymer dispersed liquid crystal, a ferroelectric liquid crystal, an antiferroelectric liquid crystal, or the like can be used. These liquid crystal materials (liquid crystal compositions) exhibit a cholesteric phase, a smectic phase, a cubic phase, a chiral nematic phase, an isotropic phase, and the like depending on conditions.

Alternatively, a liquid crystal composition exhibiting a blue phase for which an alignment film is unnecessary may be used for the liquid crystal layer 4008. The blue phase is one of the liquid crystal phases. When the temperature of the cholesteric liquid crystal is increased, the blue phase appears immediately before the transition from the cholesteric phase to the isotropic phase. The blue phase can be expressed using a liquid crystal composition in which a liquid crystal and a chiral agent are mixed. In addition, in order to widen the temperature range in which the blue phase develops, a liquid crystal layer is formed by adding a polymerizable monomer, a polymerization initiator, or the like to the liquid crystal composition that develops the blue phase, and performing a polymer stabilization treatment. You can also. A liquid crystal composition that develops a blue phase has a short response speed and is optically isotropic, so alignment treatment is unnecessary and viewing angle dependency is small. Further, since it is not necessary to provide an alignment film, a rubbing process is not required, so that electrostatic breakdown caused by the rubbing process can be prevented, and defects or breakage of the liquid crystal display device during the manufacturing process can be reduced. . Therefore, the productivity of the liquid crystal display device can be improved. In a transistor using an oxide semiconductor film, the electrical characteristics of the transistor may fluctuate significantly due to the influence of static electricity and deviate from the design range. Therefore, it is more effective to use a liquid crystal composition exhibiting a blue phase for a liquid crystal display device including a transistor including an oxide semiconductor film.

The specific resistance of the liquid crystal material is 1 × 10 ⁹ Ω · cm or more, preferably 1 × 10 ¹¹ Ω · cm or more, and more preferably 1 × 10 ¹² Ω · cm or more. In addition, the value of the specific resistance in this specification shall be the value measured at 20 degreeC.

The size of the storage capacitor provided in the liquid crystal display device is set so that charges can be held for a predetermined period in consideration of a leakage current of a transistor arranged in the pixel portion. The size of the storage capacitor may be set in consideration of the off-state current of the transistor. By using a transistor having a high-purity crystalline oxide semiconductor film, it is sufficient to provide a storage capacitor having a capacity of 1/3 or less, preferably 1/5 or less of the liquid crystal capacity of each pixel. It is.

In the transistor including the highly purified crystalline oxide semiconductor film used in this embodiment, the current value in an off state (off-state current value) can be reduced. Therefore, the holding time of an electric signal such as an image signal can be increased, and the writing interval can be set longer in the power-on state. Therefore, since the frequency of the refresh operation can be reduced, there is an effect of suppressing power consumption.

In addition, a transistor including a highly purified crystalline oxide semiconductor film used in this embodiment can have a relatively high field-effect mobility, and thus can be driven at high speed. For example, by using such a transistor capable of high-speed driving for a liquid crystal display device, the switching transistor in the pixel portion and the driver transistor used in the driver circuit portion can be formed over the same substrate. That is, since it is not necessary to use a semiconductor device formed of a silicon wafer or the like as a separate drive circuit, the number of parts of the semiconductor device can be reduced. In the pixel portion, a high-quality image can be provided by using a transistor that can be driven at high speed.

The liquid crystal display device includes a TN (Twisted Nematic) mode, an IPS (In-Plane-Switching) mode, an FFS (Fringe Field Switching) mode, an ASM (Axially Symmetrical Micro-cell) mode, and an OCB mode. An FLC (Ferroelectric Liquid Crystal) mode, an AFLC (Anti Ferroelectric Liquid Crystal) mode, or the like can be used.

Alternatively, a normally black liquid crystal display device such as a transmissive liquid crystal display device employing a vertical alignment (VA) mode may be used. There are several examples of the vertical alignment mode. For example, an MVA (Multi-Domain Vertical Alignment) mode, a PVA (Patterned Vertical Alignment) mode, an ASV (Advanced Super View) mode, and the like can be used. The present invention can also be applied to a VA liquid crystal display device. A VA liquid crystal display device is a type of a method for controlling the alignment of liquid crystal molecules of a liquid crystal display panel. The VA liquid crystal display device is a method in which liquid crystal molecules face a vertical direction with respect to a panel surface when no voltage is applied. Further, a method called multi-domain or multi-domain design in which pixels (pixels) are divided into several regions (sub-pixels) and molecules are tilted in different directions can be used.

In the display device, a black matrix (light shielding layer), a polarizing member, a retardation member, an optical member (an optical substrate) such as an antireflection member, and the like are provided as appropriate. For example, circularly polarized light using a polarizing substrate and a retardation substrate may be used. Further, a backlight, a sidelight, or the like may be used as the light source.

As a display method in the pixel portion, a progressive method, an interlace method, or the like can be used. Further, the color elements controlled by the pixels when performing color display are not limited to three colors of RGB (R represents red, G represents green, and B represents blue). For example, there is RGBW (W represents white) or RGB in which one or more colors of yellow, cyan, magenta, etc. are added. The size of the display area may be different for each dot of the color element. Note that the disclosed invention is not limited to a display device for color display, and can be applied to a display device for monochrome display.

In addition, as a display element included in the display device, a light-emitting element utilizing electroluminescence can be used. A light-emitting element using electroluminescence is distinguished depending on whether the light-emitting material is an organic compound or an inorganic compound. Generally, the former is called an organic EL element and the latter is called an inorganic EL element.

In the organic EL element, by applying a voltage to the light emitting element, electrons and holes are respectively injected from the pair of electrodes into the layer containing the light emitting organic compound, and a current flows. Then, these carriers (electrons and holes) recombine, whereby the light-emitting organic compound forms an excited state, and emits light when the excited state returns to the ground state. Due to such a mechanism, such a light-emitting element is referred to as a current-excitation light-emitting element.

Inorganic EL elements are classified into a dispersion-type inorganic EL element and a thin-film inorganic EL element depending on the element structure. The dispersion-type inorganic EL element has a light-emitting layer in which particles of a light-emitting material are dispersed in a binder, and the light emission mechanism is donor-acceptor recombination light emission using a donor level and an acceptor level. The thin-film inorganic EL element has a structure in which a light emitting layer is sandwiched between dielectric layers and further sandwiched between electrodes, and the light emission mechanism is localized light emission utilizing inner-shell electron transition of metal ions. Note that description is made here using an organic EL element as a light-emitting element.

In order to extract light emitted from the light-emitting element, at least one of the pair of electrodes may be light-transmitting. Then, a transistor and a light emitting element are formed over the substrate, and a top emission that extracts light from a surface opposite to the substrate, a bottom emission that extracts light from a surface on the substrate side, and a surface opposite to the substrate side and the substrate. There is a light-emitting element having a dual emission structure in which light emission is extracted from the light-emitting element, and any light-emitting element having an emission structure can be applied.

FIG. 14B illustrates an example of a light-emitting device using a light-emitting element as a display element. A light-emitting element 4513 which is a display element is electrically connected to a transistor 4010 provided in the pixel portion 4002. Note that although the structure of the light-emitting element 4513 is a stacked structure of the first electrode layer 4030, the electroluminescent layer 4511, and the second electrode layer 4031, it is not limited to the structure shown. The structure of the light-emitting element 4513 can be changed as appropriate depending on the direction in which light is extracted from the light-emitting element 4513, or the like.

A partition wall 4510 is formed using an organic insulating material or an inorganic insulating material. In particular, a photosensitive resin material is preferably used so that an opening is formed over the first electrode layer 4030 and the side wall of the opening has an inclined surface formed with a continuous curvature.

The electroluminescent layer 4511 may be composed of a single layer or a plurality of layers stacked.

A protective film may be formed over the second electrode layer 4031 and the partition wall 4510 so that oxygen, hydrogen, moisture, carbon dioxide, or the like does not enter the light-emitting element 4513. As the protective film, a silicon nitride film, a silicon nitride oxide film, a DLC film, or the like can be formed. In addition, a filler 4514 is provided in a space sealed by the first substrate 4001, the second substrate 4006, and the sealant 4005 and sealed. Thus, it is preferable to package (enclose) with a protective film (bonded film, ultraviolet curable resin film, etc.) or a cover material that has high air tightness and little degassing so as not to be exposed to the outside air.

In addition to an inert gas such as nitrogen or argon, an ultraviolet curable resin or a thermosetting resin can be used as the filler 4514. PVC (polyvinyl chloride), acrylic, polyimide, epoxy resin, silicone resin, PVB (polyvinyl chloride) Butyl) or EVA (ethylene vinyl acetate) can be used. For example, nitrogen may be used as the filler.

If necessary, an optical film such as a polarizing plate, a circular polarizing plate (including an elliptical polarizing plate), a retardation plate (λ / 4 plate, λ / 2 plate), a color filter, or the like is provided on the light emitting element exit surface. You may provide suitably. Further, an antireflection film may be provided on the polarizing plate or the circularly polarizing plate. For example, anti-glare treatment can be performed that diffuses reflected light due to surface irregularities and reduces reflection.

In addition, as a display device, electronic paper that drives electronic ink can be provided. Electronic paper is also called an electrophoretic display device (electrophoretic display), and has the same readability as paper, low power consumption compared to other display devices, and the advantage that it can be made thin and light. ing.

The electrophoretic display device may have various forms, and a plurality of microcapsules including first particles having a positive charge and second particles having a negative charge are dispersed in a solvent or a solute. By applying an electric field to the microcapsule, the particles in the microcapsule are moved in opposite directions to display only the color of the particles assembled on one side. Note that the first particle or the second particle contains a dye and does not move in the absence of an electric field. In addition, the color of the first particles and the color of the second particles are different (including colorless).

As described above, the electrophoretic display device is a display using a so-called dielectrophoretic effect in which a substance having a high dielectric constant moves to a high electric field region.

A solution in which the above microcapsules are dispersed in a solvent is referred to as electronic ink. This electronic ink can be printed on a surface of glass, plastic, cloth, paper, or the like. Color display is also possible by using particles having color filters or pigments.

Note that the first particle and the second particle in the microcapsule are a conductor material, an insulator material, a semiconductor material, a magnetic material, a liquid crystal material, a ferroelectric material, an electroluminescent material, an electrochromic material, or a magnetophoresis. A kind of material selected from the materials or a composite material thereof may be used.

In addition, a display device using a twisting ball display system can be used as the electronic paper. The twist ball display method is a method in which spherical particles separately painted in white and black are arranged between a first electrode layer and a second electrode layer which are electrode layers used for a display element, and the first electrode layer and the second electrode layer are arranged. In this method, display is performed by controlling the orientation of spherical particles by generating a potential difference between the two electrode layers.

13 and 14, as the first substrate 4001 and the second substrate 4006, a flexible substrate can be used in addition to a glass substrate. For example, a light-transmitting plastic substrate or the like can be used. Can be used. As the plastic, an FRP (Fiberglass-Reinforced Plastics) plate, a PVF (polyvinyl fluoride) film, a polyester film, or an acrylic resin film can be used. In addition, a metal substrate (metal film) such as aluminum or stainless steel may be used if translucency is not necessary. For example, a sheet having a structure in which an aluminum foil is sandwiched between PVF films or polyester films can be used.

In this embodiment, an aluminum oxide film is used as the insulating film 4020. The insulating film 4020 can be formed by a sputtering method or a plasma CVD method.

The aluminum oxide film provided as the insulating film 4020 over the oxide semiconductor film has a high blocking effect (blocking effect) that prevents the film from permeating both impurities such as hydrogen and moisture and oxygen.

Therefore, an aluminum oxide film is a mixture of impurities such as hydrogen and moisture, which cause fluctuations, in an oxide semiconductor film during and after the manufacturing process, and an oxide of oxygen that is a main component material of the oxide semiconductor. It functions as a protective film that prevents emission from the semiconductor film.

The transistor 4010 and the transistor 4011 each include a crystalline oxide semiconductor film obtained by crystallizing an amorphous oxide semiconductor film in which the crystalline oxide semiconductor film is oxygen-excessed by an oxygen introduction step. Since the heat treatment for crystallizing the amorphous oxide semiconductor film is performed while being covered with the aluminum oxide film, oxygen is released from the amorphous oxide semiconductor film by the heat treatment for crystallization. Can be prevented. Therefore, the obtained crystalline oxide semiconductor film maintains the oxygen content of the amorphous oxide semiconductor film, and the oxide semiconductor has an excessive oxygen content with respect to the stoichiometric composition ratio in the crystalline state. The film can include a region.

Therefore, the formed crystalline oxide semiconductor film has high purity because impurities such as hydrogen and moisture are not mixed, and oxygen release is prevented, so that the oxide semiconductor has a stoichiometric composition ratio in a crystalline state. , A film including a region having an excessive oxygen content can be obtained. Therefore, when the crystalline oxide semiconductor film is used for the transistor 4010 and the transistor 4011, variation in the threshold voltage Vth of the transistor due to oxygen deficiency and threshold voltage shift ΔVth can be reduced.

The insulating film 4021 functioning as a planarization insulating film can be formed using a heat-resistant organic material such as acrylic, polyimide, benzocyclobutene resin, polyamide, or epoxy. In addition to the organic material, a low dielectric constant material (low-k material), a siloxane resin, PSG (phosphorus glass), BPSG (phosphorus boron glass), or the like can be used. Note that the insulating film may be formed by stacking a plurality of insulating films formed using these materials.

There is no particular limitation on the formation method of the insulating film 4021. Depending on the material, a sputtering method, an SOG method, spin coating, dip coating, spray coating, a droplet discharge method (such as an inkjet method), or a printing method (screen printing or offset). Printing, etc.), doctor knives, roll coaters, curtain coaters, knife coaters and the like.

The display device performs display by transmitting light from a light source or a display element. Therefore, thin films such as a substrate, an insulating film, and a conductive film provided in the pixel portion where light is transmitted have light-transmitting properties with respect to light in the visible wavelength region.

In the first electrode layer and the second electrode layer (also referred to as a pixel electrode layer, a common electrode layer, a counter electrode layer, or the like) that applies a voltage to the display element, the direction of light to be extracted, the place where the electrode layer is provided, and What is necessary is just to select translucency and reflectivity by the pattern structure of an electrode layer.

The first electrode layer 4030 and the second electrode layer 4031 include indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, and indium. A light-transmitting conductive material such as tin oxide, indium zinc oxide, indium tin oxide to which silicon oxide is added, or graphene can be used.

The first electrode layer 4030 and the second electrode layer 4031 are tungsten (W), molybdenum (Mo), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), and tantalum (Ta). , Chromium (Cr), cobalt (Co), nickel (Ni), titanium (Ti), platinum (Pt), aluminum (Al), copper (Cu), silver (Ag), or other metals, or alloys thereof, or One or more metal nitrides can be used.

Alternatively, the first electrode layer 4030 and the second electrode layer 4031 can be formed using a conductive composition including a conductive high molecule (also referred to as a conductive polymer). As the conductive polymer, a so-called π-electron conjugated conductive polymer can be used. For example, polyaniline or a derivative thereof, polypyrrole or a derivative thereof, polythiophene or a derivative thereof, a copolymer of two or more of aniline, pyrrole, and thiophene or a derivative thereof can be given.

In addition, since the transistor is easily broken by static electricity or the like, it is preferable to provide a protective circuit for protecting the driving circuit. The protection circuit is preferably configured using a non-linear element.

As described above, by using any of the transistors described in any of Embodiments 1 to 10, a semiconductor device having various functions can be provided.

(Embodiment 12)
A semiconductor device having an image sensor function of reading information on an object can be manufactured using the transistor described as an example in any of Embodiments 1 to 10.

FIG. 15A illustrates an example of a semiconductor device having an image sensor function. FIG. 15A is an equivalent circuit of a photosensor, and FIG. 15B is a cross-sectional view illustrating part of the photosensor.

In the photodiode 602, one electrode is electrically connected to the photodiode reset signal line 658 and the other electrode is electrically connected to the gate of the transistor 640. In the transistor 640, one of a source and a drain is electrically connected to the photosensor reference signal line 672, and the other of the source and the drain is electrically connected to one of the source and the drain of the transistor 656. The transistor 656 has a gate electrically connected to the gate signal line 659 and the other of the source and the drain electrically connected to the photosensor output signal line 671.

Note that in a circuit diagram in this specification, a symbol of a transistor using an oxide semiconductor film is described as “OS” so that the transistor can be clearly identified as a transistor using an oxide semiconductor film. In FIG. 15A, the transistor described in any of Embodiments 1 to 10 can be applied to the transistor 640 and the transistor 656, which are transistors each using a crystalline oxide semiconductor film. In this embodiment, an example in which a transistor having a structure similar to that of the transistor 410 described in Embodiment 1 is used is described.

FIG. 15B is a cross-sectional view of the photodiode 602 and the transistor 640 in the photosensor. The photodiode 602 and the transistor 640 functioning as a sensor are provided over a substrate 601 (TFT substrate) having an insulating surface. Yes. A substrate 613 is provided over the photodiode 602 and the transistor 640 by using an adhesive layer 608.

An insulating film 631, an insulating film 632, an interlayer insulating film 633, and an interlayer insulating film 634 are provided over the transistor 640. The photodiode 602 is provided over the interlayer insulating film 633, and from the interlayer insulating film 633 side between the electrode layer 641 formed over the interlayer insulating film 633 and the electrode layer 642 provided over the interlayer insulating film 634. The first semiconductor film 606a, the second semiconductor film 606b, and the third semiconductor film 606c are sequentially stacked.

The electrode layer 641 is electrically connected to the conductive layer 643 formed in the interlayer insulating film 634, and the electrode layer 642 is electrically connected to the conductive layer 645 through the electrode layer 641. The conductive layer 645 is electrically connected to the gate electrode layer of the transistor 640, and the photodiode 602 is electrically connected to the transistor 640.

Here, a semiconductor film having a p-type conductivity type as the first semiconductor film 606a, a high-resistance semiconductor film (I-type semiconductor film) as the second semiconductor film 606b, and an n-type conductivity type as the third semiconductor film 606c. A pin type photodiode in which a semiconductor film having the same is stacked is illustrated.

The first semiconductor film 606a is a p-type semiconductor film and can be formed using an amorphous silicon film containing an impurity element imparting p-type conductivity. The first semiconductor film 606a is formed by a plasma CVD method using a semiconductor material gas containing a Group 13 impurity element (eg, boron (B)). Silane (SiH ₄ ) may be used as the semiconductor material gas. Alternatively, Si ₂ H ₆ , SiH ₂ Cl ₂ , SiHCl ₃ , SiCl ₄ , SiF _4, or the like may be used. Alternatively, after an amorphous silicon film not containing an impurity element is formed, the impurity element may be introduced into the amorphous silicon film by a diffusion method or an ion implantation method. It is preferable to diffuse the impurity element by introducing an impurity element by an ion implantation method or the like and then performing heating or the like. In this case, as a method for forming the amorphous silicon film, an LPCVD method, a vapor phase growth method, a sputtering method, or the like may be used. The first semiconductor film 606a is preferably formed to have a thickness greater than or equal to 10 nm and less than or equal to 50 nm.

The second semiconductor film 606b is an I-type semiconductor film (intrinsic semiconductor film) and is formed of an amorphous silicon film. For the formation of the second semiconductor film 606b, an amorphous silicon film is formed by a plasma CVD method using a semiconductor material gas. Silane (SiH ₄ ) may be used as the semiconductor material gas. Alternatively, Si ₂ H ₆ , SiH ₂ Cl ₂ , SiHCl ₃ , SiCl ₄ , SiF _4, or the like may be used. The second semiconductor film 606b may be formed by an LPCVD method, a vapor deposition method, a sputtering method, or the like. The second semiconductor film 606b is preferably formed to have a thickness greater than or equal to 200 nm and less than or equal to 1000 nm.

The third semiconductor film 606c is an n-type semiconductor film and is formed using an amorphous silicon film containing an impurity element imparting n-type conductivity. The third semiconductor film 606c is formed by a plasma CVD method using a semiconductor material gas containing a Group 15 impurity element (eg, phosphorus (P)). Silane (SiH ₄ ) may be used as the semiconductor material gas. Alternatively, Si ₂ H ₆ , SiH ₂ Cl ₂ , SiHCl ₃ , SiCl ₄ , SiF _4, or the like may be used. Alternatively, after an amorphous silicon film not containing an impurity element is formed, the impurity element may be introduced into the amorphous silicon film by a diffusion method or an ion implantation method. It is preferable to diffuse the impurity element by introducing an impurity element by an ion implantation method or the like and then performing heating or the like. In this case, as a method for forming the amorphous silicon film, an LPCVD method, a vapor phase growth method, a sputtering method, or the like may be used. The third semiconductor film 606c is preferably formed to have a thickness greater than or equal to 20 nm and less than or equal to 200 nm.

In addition, the first semiconductor film 606a, the second semiconductor film 606b, and the third semiconductor film 606c may be formed using a polycrystalline semiconductor instead of an amorphous semiconductor, or may be formed using a microcrystalline (Semi Amorphous Semiconductor: SAS)) may be formed using a semiconductor.

A microcrystalline semiconductor belongs to a metastable state between an amorphous state and a single crystal state in consideration of Gibbs free energy. That is, it is a semiconductor having a third state that is stable in terms of free energy, and has a short-range order and lattice distortion. Columnar or needle-like crystals grow in the normal direction with respect to the substrate surface. Microcrystalline silicon which is a typical example of a microcrystalline semiconductor has a Raman spectrum shifted to a lower wave number side than 520 cm ⁻¹ indicating single crystal silicon. That is, the peak of the Raman spectrum of microcrystalline silicon is between 520 cm ⁻¹ indicating single crystal silicon and 480 cm ⁻¹ indicating amorphous silicon. In addition, at least 1 atomic% or more of hydrogen or halogen is contained to terminate dangling bonds (dangling bonds). Further, by adding a rare gas element such as helium, argon, krypton, or neon to further promote lattice distortion, stability can be improved and a good microcrystalline semiconductor film can be obtained.

This microcrystalline semiconductor film can be formed by a high-frequency plasma CVD method with a frequency of several tens to several hundreds of MHz or a microwave plasma CVD apparatus with a frequency of 1 GHz or more. Typically, a silicon-containing compound such as SiH ₄ , Si ₂ H ₆ , SiH ₂ Cl ₂ , SiHCl ₃ , SiCl ₄ , or SiF ₄ can be formed by diluting with hydrogen. In addition to a compound containing silicon (eg, silicon hydride) and hydrogen, the microcrystalline semiconductor film can be formed by dilution with one or more kinds of rare gas elements selected from helium, argon, krypton, and neon. . At this time, the flow rate ratio of hydrogen to the compound containing silicon (for example, silicon hydride) is 5 to 200 times, preferably 50 to 150 times, and more preferably 100 times. Furthermore, carbide gas such as CH ₄ and C ₂ H ₆ , germanium gas such as GeH ₄ and GeF ₄ , F _{2 and the} like may be mixed in a gas containing silicon.

Further, since the mobility of holes generated by the photoelectric effect is smaller than the mobility of electrons, the pin type photodiode exhibits better characteristics when the p type semiconductor film side is the light receiving surface. Here, an example is shown in which light received by the photodiode 602 from the surface of the substrate 601 on which the pin-type photodiode is formed is converted into an electrical signal. In addition, light from the semiconductor film side having a conductivity type opposite to that of the semiconductor film as the light-receiving surface becomes disturbance light, so that a conductive film having a light shielding property is preferably used for the electrode layer. The n-type semiconductor film side can also be used as the light receiving surface.

As the insulating film 632, the interlayer insulating film 633, and the interlayer insulating film 634, an insulating material is used. Depending on the material, a sputtering method, a plasma CVD method, an SOG method, spin coating, dipping, spray coating, and droplet discharge are used. It can be formed using a method (inkjet method or the like), a printing method (screen printing, offset printing or the like), a doctor knife, a roll coater, a curtain coater, a knife coater or the like.

In this embodiment, an aluminum oxide film is used as the insulating film 631. The insulating film 631 can be formed by a sputtering method or a plasma CVD method.

The aluminum oxide film provided as the insulating film 631 over the oxide semiconductor film has a high blocking effect (blocking effect) that prevents the film from permeating both impurities such as hydrogen and moisture and oxygen.

Therefore, an aluminum oxide film is a mixture of impurities such as hydrogen and moisture, which cause fluctuations, in an oxide semiconductor film during and after the manufacturing process, and an oxide of oxygen that is a main component material of the oxide semiconductor. It functions as a protective film that prevents emission from the semiconductor film.

In this embodiment, the transistor 640 includes a crystalline oxide semiconductor film obtained by crystallizing an amorphous oxide semiconductor film into which oxygen is excessively introduced. Since the heat treatment for crystallizing the amorphous oxide semiconductor film is performed while being covered with the aluminum oxide film, oxygen is released from the amorphous oxide semiconductor film by the heat treatment for crystallization. Can be prevented. Therefore, the obtained crystalline oxide semiconductor film maintains the oxygen content of the amorphous oxide semiconductor film, and the oxide semiconductor has an excessive oxygen content with respect to the stoichiometric composition ratio in the crystalline state. The film can include a region.

Accordingly, a crystalline oxide semiconductor film to be formed has high purity because impurities such as hydrogen and moisture are not mixed and oxygen release is prevented, and the oxide semiconductor has a stoichiometric composition ratio in a crystalline state. On the other hand, a film including a region where the oxygen content is excessive can be obtained. Therefore, when the crystalline oxide semiconductor film is used for the transistor 640, variation in threshold voltage Vth of the transistor due to oxygen deficiency and threshold voltage shift ΔVth can be reduced.

As the insulating film 632, an inorganic insulating material includes an oxide insulating film such as a silicon oxide layer, a silicon oxynitride layer, an aluminum oxide layer, or an aluminum oxynitride layer, a silicon nitride layer, a silicon nitride oxide layer, an aluminum nitride layer, Alternatively, a single layer or a stacked layer of a nitride insulating film such as an aluminum nitride oxide layer can be used.

As the interlayer insulating films 633 and 634, an insulating film functioning as a planarizing insulating film is preferable in order to reduce surface unevenness. As the interlayer insulating films 633 and 634, a heat-resistant organic insulating material such as polyimide, acrylic resin, benzocyclobutene resin, polyamide, or epoxy resin can be used. In addition to the organic insulating material, a single layer or a stacked layer such as a low dielectric constant material (low-k material), a siloxane-based resin, PSG (phosphorus glass), or BPSG (phosphorus boron glass) can be used.

By detecting light incident on the photodiode 602, information on the object to be detected can be read. Note that a light source such as a backlight can be used when reading information on the object to be detected.

As described above, a transistor including a crystalline oxide semiconductor film which is highly purified and contains oxygen excessively to fill oxygen vacancies is electrically stable because variation in electrical characteristics of the transistor is suppressed. Therefore, a highly reliable semiconductor device can be provided by using the transistor.

This embodiment can be implemented in appropriate combination with the structures described in the other embodiments.

(Embodiment 13)
The transistor whose example is described in any of Embodiments 1 to 10 can be favorably used for a semiconductor device including an integrated circuit in which a plurality of transistors are stacked. In this embodiment, an example of a storage medium (memory element) is shown as an example of a semiconductor device.

The embodiment includes a transistor 140 that is a first transistor manufactured over a single crystal semiconductor substrate and a transistor 162 that is a second transistor manufactured using a semiconductor film over the transistor 140 with an insulating film interposed therebetween. A semiconductor device is manufactured. The transistor whose example is described in any of Embodiments 1 to 10 can be favorably used for the transistor 162. In this embodiment, an example in which a transistor having a structure similar to that of the transistor 440 described in Embodiment 5 is used as the transistor 162 is described.

The semiconductor materials and structures of the stacked transistors 140 and 162 may be the same or different. In this embodiment, transistors each having a material and a structure suitable for a circuit of a storage medium (memory element) are used.

FIG. 12 illustrates an example of a structure of a semiconductor device. 12A illustrates a cross section of the semiconductor device, and FIG. 12B illustrates a plan view of the semiconductor device. Here, FIG. 12A corresponds to a cross section taken along lines C1-C2 and D1-D2 in FIG. FIG. 12C illustrates an example of a circuit diagram in the case where the above semiconductor device is used as a memory element. The semiconductor device illustrated in FIGS. 12A and 12B includes a transistor 140 using a first semiconductor material in a lower portion and a transistor 162 using a second semiconductor material in an upper portion. In this embodiment, the first semiconductor material is a semiconductor material other than an oxide semiconductor, and the second semiconductor material is an oxide semiconductor. As a semiconductor material other than an oxide semiconductor, for example, silicon, germanium, silicon germanium, silicon carbide, gallium arsenide, or the like can be used, and a single crystal semiconductor is preferably used. In addition, an organic semiconductor material or the like may be used. A transistor using such a semiconductor material can easily operate at high speed. On the other hand, a transistor including an oxide semiconductor can hold charge for a long time due to its characteristics.

A method for manufacturing the semiconductor device in FIGS. 12A to 12C is described with reference to FIGS.

The transistor 140 includes a channel formation region 116 provided in a substrate 185 containing a semiconductor material (eg, silicon), an impurity region 120 provided so as to sandwich the channel formation region 116, and a metal compound region in contact with the impurity region 120. 124, a gate insulating film 108 provided over the channel formation region 116, and a gate electrode 110 provided over the gate insulating film 108.

As the substrate 185 including a semiconductor material, a single crystal semiconductor substrate such as silicon or silicon carbide, a polycrystalline semiconductor substrate, a compound semiconductor substrate such as silicon germanium, an SOI substrate, or the like can be used. In general, an “SOI substrate” refers to a substrate having a structure in which a silicon semiconductor film is provided on an insulating surface. In this specification and the like, a semiconductor film made of a material other than silicon is provided on an insulating surface. Also includes a substrate of construction. That is, the semiconductor film included in the “SOI substrate” is not limited to the silicon semiconductor film. The SOI substrate includes a substrate in which a semiconductor film is provided over an insulating substrate such as a glass substrate with an insulating film interposed therebetween.

As a method for manufacturing an SOI substrate, oxygen ions are implanted into a mirror-polished wafer and then heated at a high temperature to form an oxide layer at a certain depth from the surface and to eliminate defects generated in the surface layer. A method, a method of cleaving a semiconductor substrate using growth by heat treatment of microvoids formed by hydrogen ion irradiation, a method of forming a single crystal semiconductor film by crystal growth on an insulating surface, or the like can be used.

For example, ions are added from one surface of a single crystal semiconductor substrate to form a weakened layer at a certain depth from one surface of the single crystal semiconductor substrate, and one element of the single crystal semiconductor substrate or element An insulating film is formed on one of the substrates. In a state where the single crystal semiconductor substrate and the element substrate are overlapped with an insulating film interposed therebetween, a crack is generated in the weakened layer, and heat treatment is performed to separate the single crystal semiconductor substrate with the weakened layer, and the semiconductor is removed from the single crystal semiconductor substrate. A single crystal semiconductor film is formed over the element substrate as a film. An SOI substrate manufactured by using the above method can also be preferably used.

An element isolation insulating layer 106 is provided over the substrate 185 so as to surround the transistor 140. Note that in order to achieve high integration, it is preferable that the transistor 140 have no sidewall insulating layer as a sidewall as illustrated in FIG. On the other hand, when importance is attached to the characteristics of the transistor 140, a sidewall insulating layer serving as a sidewall may be provided on the side surface of the gate electrode 110, and the impurity region 120 including regions having different impurity concentrations may be provided.

The transistor 140 using a single crystal semiconductor substrate can operate at high speed. Therefore, information can be read at high speed by using the transistor as a reading transistor. Two insulating films are formed so as to cover the transistor 140. As a process before the formation of the transistor 162 and the capacitor 164, the insulating film 2 layer is subjected to CMP to form the planarized insulating film 128 and the insulating film 130, and the upper surface of the gate electrode 110 is exposed at the same time.

The insulating film 128 and the insulating film 130 are typically a silicon oxide film, a silicon oxynitride film, an aluminum oxide film, an aluminum oxynitride film, a silicon nitride film, an aluminum nitride film, a silicon nitride oxide film, an aluminum nitride oxide film, or the like. An inorganic insulating film can be used. The insulating film 128 and the insulating film 130 can be formed by a plasma CVD method, a sputtering method, or the like.

Alternatively, an organic material such as polyimide, acrylic resin, or benzocyclobutene resin can be used. In addition to the organic material, a low dielectric constant material (low-k material) or the like can be used. In the case of using an organic material, the insulating film 128 and the insulating film 130 may be formed by a wet method such as a spin coating method or a printing method.

Note that a silicon oxide film is used as the insulating film 130 in contact with the semiconductor film.

In this embodiment, a 50-nm-thick silicon oxynitride film is formed as the insulating film 128 by a sputtering method, and a 550-nm-thick silicon oxide film is formed as the insulating film 130 by a sputtering method.

A semiconductor film is formed over the insulating film 130 which is sufficiently planarized by CMP treatment. In this embodiment, the oxide semiconductor includes a region in which the oxygen content is excessive with respect to the stoichiometric composition ratio in the crystalline state by a sputtering method using an In—Ga—Zn-based oxide target as the semiconductor film. An amorphous oxide semiconductor film is formed.

Next, the amorphous oxide semiconductor film is selectively etched to form an island-shaped amorphous oxide semiconductor film, and an oxygen introduction step is performed on the amorphous oxide semiconductor film. A gate insulating film 146, a gate electrode layer 148, and sidewall insulating layers 136a and 136b are formed over the amorphous oxide semiconductor film.

As the gate insulating film 146, a silicon oxide film, a silicon nitride film, a silicon oxynitride film, a silicon nitride oxide film, an aluminum oxide film, an aluminum nitride film, an aluminum oxynitride film, a nitrided oxide film, or the like is used by a plasma CVD method or a sputtering method. An aluminum film, a hafnium oxide film, or a gallium oxide film can be formed.

The gate electrode layer 148 can be formed by forming a conductive layer over the gate insulating film 146 and then selectively etching the conductive layer.

Next, a conductive layer is formed over the gate electrode 110, the insulating film 128, the insulating film 130, and the like, and the conductive layer is selectively etched to form a source or drain electrode 142a and a source or drain electrode 142b. To do.

The conductive layer can be formed by a PVD method such as a sputtering method or a CVD method such as a plasma CVD method. As a material for the conductive layer, an element selected from Al, Cr, Cu, Ta, Ti, Mo, and W, an alloy containing the above-described element as a component, or the like can be used. Any of Mn, Mg, Zr, Be, Nd, Sc, or a material obtained by combining a plurality of these may be used.

The conductive layer may have a single layer structure or a stacked structure of two or more layers. For example, a single-layer structure of a titanium film or a titanium nitride film, a single-layer structure of an aluminum film containing silicon, a two-layer structure in which a titanium film is laminated on an aluminum film, or a two-layer structure in which a titanium film is laminated on a titanium nitride film Examples thereof include a three-layer structure in which a titanium film, an aluminum film, and a titanium film are stacked. Note that in the case where the conductive layer has a single-layer structure of a titanium film or a titanium nitride film, there is a merit that processing into the source or drain electrode 142a having a tapered shape and the source or drain electrode 142b is easy. is there.

Next, the insulating film 150 including an aluminum oxide film is formed over the amorphous oxide semiconductor film, the gate insulating film 146, the gate electrode layer 148, and the sidewall insulating layers 136a and 136b. In the case where the insulating film 150 has a stacked structure, a plasma CVD method, a sputtering method, or the like is used to form a silicon oxide film, a silicon nitride film, a silicon oxynitride film, a silicon nitride oxide film, an aluminum nitride film, an aluminum oxynitride film, or a oxynitride film An aluminum film, a hafnium oxide film, or a gallium oxide film may be stacked with the aluminum oxide film.

Next, heat treatment is performed on the amorphous oxide semiconductor film, and at least a part of the amorphous oxide semiconductor film is crystallized to include crystalline oxide including crystals having a c-axis substantially perpendicular to the surface. A physical semiconductor film 144 is formed.

The aluminum oxide film provided as the insulating film 150 over the oxide semiconductor film has a high blocking effect (blocking effect) that prevents the film from passing through both impurities such as hydrogen and moisture, and oxygen.

Therefore, an aluminum oxide film is a mixture of impurities such as hydrogen and moisture, which cause fluctuations, in an oxide semiconductor film during and after the manufacturing process, and an oxide of oxygen that is a main component material of the oxide semiconductor. It functions as a protective film that prevents emission from the semiconductor film.

Since the heat treatment for crystallizing the amorphous oxide semiconductor film is performed in a state of being covered with the aluminum oxide film provided as the insulating film 150, the heat treatment for crystallization is performed from the amorphous oxide semiconductor film. Oxygen can be prevented from being released. Therefore, the obtained crystalline oxide semiconductor film 144 maintains the amount of oxygen contained in the amorphous oxide semiconductor film, and the oxide semiconductor has an excessive oxygen content with respect to the stoichiometric composition ratio in the crystalline state. It is possible to form a film including various regions.

Accordingly, the formed crystalline oxide semiconductor film 144 has high purity because impurities such as hydrogen and moisture are not mixed therein, and oxygen oxide is prevented from being released, so that the oxide semiconductor has a stoichiometric composition ratio in a crystalline state. On the other hand, it includes a region where the oxygen content is excessive. Therefore, when the crystalline oxide semiconductor film 144 is used for the transistor 162, variation in threshold voltage Vth of the transistor due to oxygen deficiency and threshold voltage shift ΔVth can be reduced.

The temperature of heat treatment for crystallizing at least part of the amorphous oxide semiconductor film is 250 ° C to 700 ° C, preferably 400 ° C or more, more preferably 500 ° C, and further preferably 550 ° C or more.

Over the insulating film 150, an electrode layer 153 is formed in a region overlapping with the source or drain electrode 142a.

Next, the insulating film 152 is formed over the transistor 162 and the insulating film 150. The insulating film 152 can be formed by a sputtering method, a CVD method, or the like. Alternatively, the insulating layer can be formed using a material including an inorganic insulating material such as silicon oxide, silicon oxynitride, silicon nitride, hafnium oxide, or aluminum oxide.

Next, an opening reaching the source or drain electrode 142b is formed in the gate insulating film 146, the insulating film 150, and the insulating film 152. The opening is formed by selective etching using a mask or the like.

After that, a wiring 156 in contact with the source or drain electrode 142b is formed in the opening. Note that FIG. 12 does not illustrate a connection portion between the source or drain electrode 142b and the wiring 156.

The wiring 156 is formed by forming a conductive layer using a PVD method such as a sputtering method or a CVD method such as a plasma CVD method, and then etching the conductive layer. As a material for the conductive layer, an element selected from Al, Cr, Cu, Ta, Ti, Mo, and W, an alloy containing the above-described element as a component, or the like can be used. Any of Mn, Mg, Zr, Be, Nd, Sc, or a material obtained by combining a plurality of these may be used. The details are similar to those of the source or drain electrode 142a.

Through the above process, the transistor 162 and the capacitor 164 are completed. The transistor 162 is a transistor including the crystalline oxide semiconductor film 144 which is highly purified and contains excess oxygen which fills oxygen vacancies. Thus, the transistor 162 is electrically stable because variation in electrical characteristics is suppressed. The capacitor 164 includes a source or drain electrode 142a, a crystalline oxide semiconductor film 144, a gate insulating film 146, and an electrode layer 153.

Note that in the capacitor 164 in FIG. 12, the crystalline oxide semiconductor film 144 and the gate insulating film 146 are stacked, so that sufficient insulation between the source or drain electrode 142 a and the electrode layer 153 is ensured. be able to. Needless to say, a capacitor 164 having a structure without the crystalline oxide semiconductor film 144 may be employed in order to ensure sufficient capacitance. Alternatively, the capacitor 164 having an insulating film may be employed. Further, in the case where a capacitor is unnecessary, a structure in which the capacitor 164 is not provided is also possible.

FIG. 12C illustrates an example of a circuit diagram in the case where the above semiconductor device is used as a memory element. In FIG. 12C, one of the source electrode and the drain electrode of the transistor 162, one of the electrodes of the capacitor 164, and the gate electrode of the transistor 140 are electrically connected. In addition, the first wiring (1st Line: also referred to as a source line) and the source electrode of the transistor 140 are electrically connected, and the second wiring (2nd Line: also referred to as a bit line) and the drain electrode of the transistor 140 are connected to each other. Are electrically connected. In addition, the third wiring (3rd Line: also referred to as a first signal line) and the other of the source electrode and the drain electrode of the transistor 162 are electrically connected, and the fourth wiring (4th Line: second signal) A gate electrode of the transistor 162 and the gate electrode of the transistor 162 are electrically connected to each other. The fifth wiring (5th Line: also called a word line) and the other electrode of the capacitor 164 are electrically connected.

Since the transistor 162 including an oxide semiconductor has a feature of extremely low off-state current, when the transistor 162 is turned off, one of a source electrode and a drain electrode of the transistor 162 and the capacitor 164 A potential of a node (hereinafter, node FG) where one of the electrodes and the gate electrode of the transistor 140 are electrically connected can be held for an extremely long time. With the capacitor 164, the charge given to the node FG can be easily held, and the held information can be easily read.

In the case of storing information in the semiconductor device (writing), first, the potential of the fourth wiring is set to a potential at which the transistor 162 is turned on, so that the transistor 162 is turned on. Accordingly, the potential of the third wiring is supplied to the node FG, and a predetermined amount of charge is accumulated in the node FG. Here, it is assumed that one of two charges (hereinafter, referred to as a low level charge and a high level charge) giving two different potential levels is given. After that, when the potential of the fourth wiring is set to a potential at which the transistor 162 is turned off and the transistor 162 is turned off, the node FG is in a floating state, so that a predetermined charge is held in the node FG. It will remain as it is. As described above, information can be stored in the memory cell by accumulating and holding a predetermined amount of charge in the node FG.

Since the off-state current of the transistor 162 is extremely small, the charge supplied to the node FG is held for a long time. Therefore, the refresh operation becomes unnecessary or the frequency of the refresh operation can be extremely reduced, and the power consumption can be sufficiently reduced. Further, stored data can be retained for a long time even when power is not supplied.

When reading stored information (reading), when a predetermined potential (constant potential) is applied to the first wiring and an appropriate potential (reading potential) is applied to the fifth wiring, the data is held in the node FG. Depending on the amount of charge made, the transistor 140 is in a different state. In general, when the transistor 140 is an n-channel transistor, the apparent threshold V _{th_H} of the transistor 140 when the high-level charge is held at the node FG is equal to the transistor when the low-level charge is held at the node FG. This is because it becomes lower than the apparent threshold value V _{th_L} of 140. Here, the apparent threshold value means a potential of the fifth wiring which is necessary for turning on the transistor 140. Therefore, the charge held in the node FG can be determined by _setting the potential of the fifth wiring to a potential V ₀ between V _{th_H} and V _{th_L} . For example, in the case where a high-level charge is applied in writing, the transistor 140 is turned “on” when the potential of the fifth wiring is V ₀ (> V _{th_H} ). When the low-level charge is _supplied , the transistor 140 remains in the “off state” even when the potential of the fifth wiring is V ₀ (<V _{th_L} ). Therefore, the stored information can be read by controlling the potential of the fifth wiring and reading the on state or the off state of the transistor 140 (reading the potential of the second wiring).

In addition, in the case of rewriting stored information, a new potential is supplied to the node FG that holds a predetermined amount of charge by the above writing, whereby the charge related to the new information is held in the node FG. Specifically, the potential of the fourth wiring is set to a potential at which the transistor 162 is turned on, so that the transistor 162 is turned on. Accordingly, the potential of the third wiring (the potential related to new information) is supplied to the node FG, and a predetermined amount of charge is accumulated in the node FG. After that, the potential of the fourth wiring is set to a potential at which the transistor 162 is turned off and the transistor 162 is turned off, so that charge related to new information is held in the node FG. That is, the stored information can be overwritten by performing the same operation (second writing) as the first writing in a state where a predetermined amount of charge is held in the node FG by the first writing. It is.

In the transistor 162 described in this embodiment, a highly purified oxide semiconductor film containing excess oxygen is used for the crystalline oxide semiconductor film 144, whereby the off-state current of the transistor 162 can be sufficiently reduced. . By using such a transistor, a semiconductor device that can hold stored data for an extremely long time can be obtained.

As described above, a transistor including a crystalline oxide semiconductor film which is highly purified and contains oxygen excessively to fill oxygen vacancies is electrically stable because variation in electrical characteristics of the transistor is suppressed. Therefore, a highly reliable semiconductor device can be provided by using the transistor.

The structures, methods, and the like described in this embodiment can be combined as appropriate with any of the structures, methods, and the like described in the other embodiments.

(Embodiment 14)
The semiconductor device disclosed in this specification can be applied to a variety of electronic devices (including game machines). Examples of the electronic device include a television device (also referred to as a television or a television receiver), a monitor for a computer, a camera such as a digital camera or a digital video camera, a digital photo frame, a mobile phone (a mobile phone or a mobile phone). Large-sized game machines such as portable game machines, portable information terminals, sound reproduction apparatuses, and pachinko machines. Examples of electronic devices each including the semiconductor device described in any of the above embodiments will be described.

FIG. 16A illustrates a laptop personal computer, which includes a main body 3001, a housing 3002, a display portion 3003, a keyboard 3004, and the like. By applying the semiconductor device described in any of Embodiments 1 to 13 to the display portion 3003, a highly reliable laptop personal computer can be obtained.

FIG. 16B illustrates a personal digital assistant (PDA). A main body 3021 is provided with a display portion 3023, an external interface 3025, operation buttons 3024, and the like. There is a stylus 3022 as an accessory for operation. By applying the semiconductor device described in any of Embodiments 1 to 13 to the display portion 3023, a highly reliable personal digital assistant (PDA) can be provided.

FIG. 16C illustrates an example of an electronic book. For example, the electronic book includes two housings, a housing 2701 and a housing 2703. The housing 2701 and the housing 2703 are integrated with a shaft portion 2711 and can be opened / closed using the shaft portion 2711 as an axis. With such a configuration, an operation like a paper book can be performed.

A display portion 2705 and a display portion 2707 are incorporated in the housing 2701 and the housing 2703, respectively. The display unit 2705 and the display unit 2707 may be configured to display a continuous screen or may be configured to display different screens. By adopting a configuration in which different screens are displayed, for example, a sentence is displayed on the right display unit (display unit 2705 in FIG. 16C) and an image is displayed on the left display unit (display unit 2707 in FIG. 16C). Can be displayed. By applying the semiconductor device described in any of Embodiments 1 to 13 to the display portion 2705 and the display portion 2707, a highly reliable electronic book can be obtained. In the case where a transflective or reflective liquid crystal display device is used as the display portion 2705, it is expected to be used in a relatively bright situation. Therefore, a solar cell is provided, and power generation by the solar cell and charging with the battery can be performed. You may do it. In addition, when a lithium ion battery is used as a battery, there exists an advantage, such as achieving size reduction.

FIG. 16C illustrates an example in which the housing 2701 is provided with an operation portion and the like. For example, the housing 2701 is provided with a power supply 2721, operation keys 2723, a speaker 2725, and the like. Pages can be turned with the operation keys 2723. Note that a keyboard, a pointing device, or the like may be provided on the same surface as the display portion of the housing. In addition, an external connection terminal (such as an earphone terminal or a USB terminal), a recording medium insertion portion, or the like may be provided on the rear surface or side surface of the housing. Further, the electronic book may have a structure as an electronic dictionary.

Further, the electronic book may have a configuration capable of transmitting and receiving information wirelessly. It is also possible to adopt a configuration in which desired book data or the like is purchased and downloaded from an electronic book server wirelessly.

FIG. 16D illustrates a mobile phone, which includes two housings, a housing 2800 and a housing 2801. The housing 2801 is provided with a display panel 2802, a speaker 2803, a microphone 2804, a pointing device 2806, a camera lens 2807, an external connection terminal 2808, and the like. The housing 2800 is provided with a solar cell 2810 for charging the mobile phone, an external memory slot 2811, and the like. An antenna is incorporated in the housing 2801. By applying the semiconductor device described in any of Embodiments 1 to 13 to the display panel 2802, a highly reliable mobile phone can be provided.

In addition, the display panel 2802 is provided with a touch panel. A plurality of operation keys 2805 which are displayed as images is illustrated by dashed lines in FIG. Note that a booster circuit for boosting the voltage output from the solar battery cell 2810 to a voltage required for each circuit is also mounted.

In the display panel 2802, the display direction can be appropriately changed depending on a usage pattern. In addition, since the camera lens 2807 is provided on the same surface as the display panel 2802, a videophone can be used. The speaker 2803 and the microphone 2804 can be used for videophone calls, recording and playing sound, and the like as well as voice calls. Further, the housing 2800 and the housing 2801 can be slid to be in an overlapped state from the developed state as illustrated in FIG. 16D, so that the size of the mobile phone can be reduced.

The external connection terminal 2808 can be connected to an AC adapter and various types of cables such as a USB cable, and charging and data communication with a personal computer are possible. Further, a recording medium can be inserted into the external memory slot 2811 so that a larger amount of data can be stored and moved.

In addition to the above functions, an infrared communication function, a television reception function, or the like may be provided.

FIG. 16E illustrates a digital video camera which includes a main body 3051, a display portion (A) 3057, an eyepiece portion 3053, operation switches 3054, a display portion (B) 3055, a battery 3056, and the like. By applying the semiconductor device described in any of Embodiments 1 to 13 to the display portion (A) 3057 and the display portion (B) 3055, a highly reliable digital video camera can be obtained.

FIG. 16F illustrates an example of a television set. In the television device, a display portion 9603 is incorporated in a housing 9601. Images can be displayed on the display portion 9603. Here, a structure in which the housing 9601 is supported by a stand 9605 is illustrated. By applying the semiconductor device described in any of Embodiments 1 to 13 to the display portion 9603, a highly reliable television device can be provided.

The television device can be operated with an operation switch provided in the housing 9601 or a separate remote controller. Further, the remote controller may be provided with a display unit that displays information output from the remote controller.

Note that the television device is provided with a receiver, a modem, and the like. General TV broadcasts can be received by a receiver, and connected to a wired or wireless communication network via a modem, so that it can be unidirectional (sender to receiver) or bidirectional (sender and receiver). It is also possible to perform information communication between each other or between recipients).

This embodiment can be implemented in appropriate combination with the structures described in the other embodiments.

In this example, the characteristics of an aluminum oxide film used as a barrier film in a semiconductor device according to the disclosed invention were evaluated. The results are shown in FIGS. As an evaluation method, secondary ion mass spectrometry (SIMS) and TDS (Thermal Desorption Spectroscopy) analysis were used.

First, the evaluation performed by SIMS analysis is shown. As a comparative example, a comparative example sample A in which a silicon oxide film by a sputtering method was formed on a glass substrate as a comparative example by a thickness of 100 nm, and a silicon oxide film by a sputtering method in a thickness of 100 nm by a sputtering method as an example. Example Sample A in which an aluminum oxide film having a thickness of 100 nm was formed on a silicon film by sputtering was prepared.

In Comparative Sample A and Example Sample A, the silicon oxide film was formed using a silicon oxide (SiO ₂ ) target as a target, a distance between the glass substrate and the target of 60 mm, a pressure of 0.4 Pa, and a power source. The substrate temperature was set to 100 ° C. in an atmosphere of 1.5 kW and oxygen (oxygen flow rate 50 sccm).

In Example Sample A, the aluminum oxide film was formed under the conditions of using an aluminum oxide (Al ₂ O ₃ ) target as a target, a distance between the glass substrate and the target of 60 mm, a pressure of 0.4 Pa, and a power source of 1.5 kW. The substrate temperature was 250 ° C. in an atmosphere of argon and oxygen (argon flow rate 25 sccm: oxygen flow rate 25 sccm).

A pressure cooker test (PCT) was performed on the comparative sample A and the example sample A. In this example, as a PCT test, a sample of a comparative example was obtained under the conditions of a temperature of 130 ° C., a humidity of 85%, H ₂ O (water): D ₂ O (heavy water) = 3: 1 atmosphere, 2.3 atm (0.23 MPa). A and Example Sample A were held for 100 hours.

Using SSDP (Substrate Side Depth Profile) -SIMS as the SIMS analysis, the H atom and D (deuterium) atom of each sample were compared with the comparative sample A and the example sample A before and after the PCT test. Concentration was measured. Note that the D atom is one of the isotopes of hydrogen, represented by chemical symbol ^{2 H.}

FIG. 17A1 shows the concentration profiles of H and D atoms by SIMS before the PCT test of Comparative Sample A, and FIG. 17A2 after the PCT test of Comparative Sample A. In FIG. 17A1 and FIG. 17A2, the D atom expected profile is a concentration profile of D atoms present in the natural world calculated from the profile of H atoms when the abundance ratio of D atoms is 0.015%. Therefore, the amount of D atoms mixed in the sample by the PCT test is the difference between the actually measured D atom concentration and the D atom expected concentration. A concentration profile of D atoms obtained by subtracting the D atom expected concentration from the actually measured D atom concentration is shown in FIG. 17B1 before the PCT test and in FIG. 17B2 after the PCT test.

Similarly, FIG. 18A1 shows the concentration profiles of H and D atoms by SIMS before the PCT test of Example Sample A and FIG. 18A2 after the PCT test of Example Sample A. Further, a concentration profile of D atoms obtained by subtracting the D atom expected concentration from the actually measured D atom concentration is shown in FIG. 18B1 before the PCT test and in FIG. 18B2 after the PCT test.

The SIMS analysis results of this example all show the results of quantification using a standard sample of a silicon oxide film.

As shown in FIG. 17, the actually measured D atom concentration profile and the D atom expected profile which overlapped before the PCT test increased to a high concentration after the PCT test. It can be seen that D atoms are mixed in the film. Therefore, it was confirmed that the silicon oxide film of the comparative example sample had a low barrier property against moisture (H ₂ O, D ₂ O) from the outside.

On the other hand, as shown in FIG. 18, the sample A in which the aluminum oxide film is laminated on the silicon oxide film shows that only a slight amount of D atoms enter the surface of the aluminum oxide film even after the PCT test. No penetration of D atoms is observed after about 30 nm and in the silicon oxide film. Therefore, it was confirmed that the aluminum oxide film has a high barrier property against moisture (H ₂ O, D ₂ O) from the outside.

Next, the evaluation performed by TDS analysis is shown. As a sample, an example sample B in which a silicon oxide film was formed to a thickness of 100 nm on a glass substrate by a sputtering method and an aluminum oxide film was formed to a thickness of 20 nm on the silicon oxide film by a sputtering method was prepared. In addition, as a comparative example, after measuring the example sample B by TDS analysis, the aluminum oxide film was removed from the example sample B, and the comparative example sample B in which only the silicon oxide film was formed on the glass substrate was produced.

In Comparative Sample B and Example Sample B, the silicon oxide film was formed using a silicon oxide (SiO ₂ ) target as a target, a distance between the glass substrate and the target of 60 mm, a pressure of 0.4 Pa, and a power source. The substrate temperature was set to 100 ° C. in an atmosphere of 1.5 kW and oxygen (oxygen flow rate 50 sccm).

In Example Sample B, the aluminum oxide film was formed using an aluminum oxide (Al ₂ O ₃ ) target as a target, a distance between the glass substrate and the target of 60 mm, a pressure of 0.4 Pa, and a power source of 1.5 kW. The substrate temperature was 250 ° C. in an atmosphere of argon and oxygen (argon flow rate 25 sccm: oxygen flow rate 25 sccm).

In Comparative Example Sample B and Example Sample B, samples were further prepared under conditions of 300 ° C. heat treatment, 450 ° C. heat treatment, and 600 ° C. heat treatment for 1 hour in a nitrogen atmosphere.

In Comparative Sample B and Example Sample B, TDS analysis was performed on samples prepared under four conditions: no heat treatment, 300 ° C. heat treatment, 450 ° C. heat treatment, and 600 ° C. heat treatment. In Comparative Sample B and Example Sample B, heat treatment was not performed in FIGS. 19A and 20A, heat treatment was performed at 300 ° C. in FIGS. 19B and 20B, and FIGS. FIG. 20C shows TDS results of measured M / z = 32 (O ₂ ) of each sample subjected to 450 ° C. heat treatment, and FIGS. 19D and 20D show heat treatment at 600 ° C. .

As shown in FIGS. 19A to 19D, the comparative sample B shows no oxygen release from the silicon oxide film in FIG. 19A without heat treatment, but is heated at 300 ° C. in FIG. 19B. In the sample subjected to the treatment, the amount of released oxygen was greatly reduced. In the sample subjected to the 450 ° C. heat treatment in FIG. 19C and the sample subjected to the 600 ° C. heat treatment in FIG. It became below the background.

19A to 19D, 90% or more of the excess oxygen contained in the silicon oxide film is released from the silicon oxide film to the outside by the heat treatment at 300 ° C., and heated at 450 ° C. and 600 ° C. It can be seen that excess oxygen contained in almost all of the silicon oxide film was released to the outside of the silicon oxide film depending on the treatment. Therefore, it was confirmed that the silicon oxide film has a low barrier property against oxygen.

On the other hand, as shown in FIGS. 20A to 20D, in Example Sample B in which an aluminum oxide film is formed on a silicon oxide film, the samples subjected to heat treatment at 300 ° C., 450 ° C., and 600 ° C. However, an oxygen release equivalent to that of the sample without heat treatment was observed.

20A to 20D, by forming an aluminum oxide film over the silicon oxide film, excess oxygen contained in the silicon oxide film is not easily released to the outside even when heat treatment is performed. It can be seen that the state contained in the silicon oxide film is maintained to a considerable extent. Therefore, it was confirmed that the aluminum oxide film has a high barrier property against oxygen.

From the above results, it was confirmed that the aluminum oxide film has both a barrier property against hydrogen and moisture and a barrier property against oxygen, and functions suitably as a barrier film against hydrogen, moisture, and oxygen.

Therefore, the aluminum oxide film is a mixture of impurities such as hydrogen and moisture, which are factors of fluctuation, into the oxide semiconductor film and a main component of the oxide semiconductor during and after the manufacturing process of the transistor including the oxide semiconductor film. It can function as a protective film for preventing release of oxygen, which is a component material, from the oxide semiconductor film.

Therefore, the formed crystalline oxide semiconductor film has high purity because impurities such as hydrogen and moisture are not mixed, and oxygen release is prevented, so that the oxide semiconductor has a stoichiometric composition ratio in a crystalline state. Including the region where the oxygen content is excessive. Therefore, when the crystalline oxide semiconductor film is used for a transistor, variation in threshold voltage Vth of the transistor due to oxygen vacancies and shift ΔVth in threshold voltage can be reduced.

Claims (2)

Forming an insulating film,
Forming an oxide semiconductor film on the insulating film;
Introducing oxygen into the oxide semiconductor film using an ion implantation method ,
After introducing oxygen, a source electrode and a drain electrode are formed on the oxide semiconductor film ,
Forming an aluminum oxide film on the source electrode and the drain electrode;
After forming the aluminum oxide film, the oxide semiconductor film is subjected to heat treatment to be crystallized to form an oxide semiconductor film including crystals. Forming an insulating film,
Forming an oxide semiconductor film on the insulating film;
Introducing oxygen into the oxide semiconductor film using an ion implantation method,
After introducing oxygen, a source electrode and a drain electrode are formed on the oxide semiconductor film,
Forming an oxide insulating film on the source electrode and the drain electrode;
Forming an aluminum oxide film on the oxide insulating film;
After forming the aluminum oxide film, the oxide semiconductor film is subjected to heat treatment to be crystallized to form an oxide semiconductor film including crystals.

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